andreachild commented on code in PR #3209:
URL: https://github.com/apache/tinkerpop/pull/3209#discussion_r2377013333


##########
gremlin-core/src/test/java/org/apache/tinkerpop/gremlin/process/traversal/step/TraversalParentTest.java:
##########
@@ -0,0 +1,1028 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.tinkerpop.gremlin.process.traversal.step;
+
+import java.time.OffsetDateTime;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+import org.apache.commons.configuration2.MapConfiguration;
+import org.apache.tinkerpop.gremlin.process.traversal.Operator;
+import org.apache.tinkerpop.gremlin.process.traversal.Pick;
+import org.apache.tinkerpop.gremlin.process.traversal.Step;
+import org.apache.tinkerpop.gremlin.process.traversal.Traversal;
+import 
org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.GraphTraversalSource;
+import org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.__;
+import 
org.apache.tinkerpop.gremlin.process.traversal.lambda.AbstractLambdaTraversal;
+import org.apache.tinkerpop.gremlin.process.traversal.lambda.ConstantTraversal;
+import org.apache.tinkerpop.gremlin.process.traversal.Merge;
+import org.apache.tinkerpop.gremlin.process.traversal.Scope;
+import org.apache.tinkerpop.gremlin.process.traversal.P;
+import org.apache.tinkerpop.gremlin.process.traversal.lambda.LoopTraversal;
+import 
org.apache.tinkerpop.gremlin.process.traversal.lambda.PredicateTraversal;
+import org.apache.tinkerpop.gremlin.process.traversal.lambda.TrueTraversal;
+import org.apache.tinkerpop.gremlin.process.traversal.lambda.ValueTraversal;
+import 
org.apache.tinkerpop.gremlin.process.traversal.step.map.AddEdgeStepContract;
+import 
org.apache.tinkerpop.gremlin.process.traversal.step.map.AddVertexStepContract;
+import 
org.apache.tinkerpop.gremlin.process.traversal.step.map.CallStepContract;
+import 
org.apache.tinkerpop.gremlin.process.traversal.step.map.MergeStepContract;
+import 
org.apache.tinkerpop.gremlin.process.traversal.step.sideEffect.AddPropertyStepContract;
+import 
org.apache.tinkerpop.gremlin.process.traversal.step.sideEffect.AggregateGlobalStep;
+import 
org.apache.tinkerpop.gremlin.process.traversal.step.sideEffect.AggregateLocalStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.filter.AndStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.filter.OrStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.branch.BranchStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.branch.ChooseStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.map.CoalesceStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.map.CombineStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.map.ConcatStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.map.DateDiffStep;
+import 
org.apache.tinkerpop.gremlin.process.traversal.step.filter.DedupGlobalStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.map.DifferenceStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.map.DisjunctStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.map.FormatStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.map.GroupCountStep;
+import 
org.apache.tinkerpop.gremlin.process.traversal.step.sideEffect.GroupCountSideEffectStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.map.GroupStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.map.IntersectStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.branch.LocalStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.map.MatchStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.map.MathStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.map.MergeStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.filter.NotStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.branch.OptionalStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.map.OrderGlobalStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.map.OrderLocalStep;
+import 
org.apache.tinkerpop.gremlin.process.traversal.step.filter.PathFilterStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.map.PathStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.map.ProductStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.map.ProjectStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.map.PropertyMapStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.branch.RepeatStep;
+import 
org.apache.tinkerpop.gremlin.process.traversal.step.sideEffect.SackValueStep;
+import 
org.apache.tinkerpop.gremlin.process.traversal.step.filter.SampleGlobalStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.map.SelectOneStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.map.SelectStep;
+import 
org.apache.tinkerpop.gremlin.process.traversal.step.map.TraversalSelectStep;
+import 
org.apache.tinkerpop.gremlin.process.traversal.step.filter.TraversalFilterStep;
+import 
org.apache.tinkerpop.gremlin.process.traversal.step.map.TraversalFlatMapStep;
+import 
org.apache.tinkerpop.gremlin.process.traversal.step.map.TraversalMapStep;
+import 
org.apache.tinkerpop.gremlin.process.traversal.step.sideEffect.TraversalSideEffectStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.map.TreeStep;
+import 
org.apache.tinkerpop.gremlin.process.traversal.step.sideEffect.TreeSideEffectStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.branch.UnionStep;
+import 
org.apache.tinkerpop.gremlin.process.traversal.step.filter.WherePredicateStep;
+import 
org.apache.tinkerpop.gremlin.process.traversal.step.filter.WhereTraversalStep;
+import 
org.apache.tinkerpop.gremlin.process.traversal.step.util.ComputerAwareStep;
+import 
org.apache.tinkerpop.gremlin.process.traversal.strategy.optimization.GValueReductionStrategy;
+import org.apache.tinkerpop.gremlin.process.traversal.util.TraversalHelper;
+import org.apache.tinkerpop.gremlin.structure.T;
+import org.apache.tinkerpop.gremlin.structure.service.Service;
+import org.apache.tinkerpop.gremlin.structure.service.ServiceRegistry;
+
+import org.apache.tinkerpop.gremlin.structure.util.GraphFactoryTest;
+import org.junit.BeforeClass;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
+
+import static 
org.apache.tinkerpop.gremlin.process.traversal.AnonymousTraversalSource.traversal;
+import static org.hamcrest.Matchers.containsInAnyOrder;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertThat;
+import static org.junit.Assert.assertTrue;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyBoolean;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+
+@RunWith(Parameterized.class)
+public class TraversalParentTest {
+
+    private static ServiceRegistry mockedRegistry= mock(ServiceRegistry.class);
+    private static Service<?, ?> mockedService = mock(Service.class);
+    private static GraphTraversalSource g = 
traversal().with(GraphFactoryTest.MockGraph.open(new 
MapConfiguration(Map.of("service-registry", mockedRegistry))));
+
+    @BeforeClass
+    public static void setupClass() {
+        when(mockedRegistry.get(any(), anyBoolean(), 
any())).thenReturn(mockedService);
+        when(mockedService.getRequirements()).thenReturn(Set.of());
+    }
+
+    @Parameterized.Parameter(value = 0)
+    public Class stepClass;
+
+    @Parameterized.Parameter(value = 1)
+    public Traversal.Admin traversal;
+
+    @Parameterized.Parameter(value = 2)
+    public List<Traversal.Admin<?,?>> expectedGlobalChildren;
+
+    @Parameterized.Parameter(value = 3)
+    public List<Traversal.Admin<?,?>> expectedLocalChildren;
+
+    /**
+     * Overrides expectedGlobalChildren for assertions following strategy 
execution. If left null, expectedGlobalChildren is used instead.
+     */
+    @Parameterized.Parameter(value = 4)
+    public List<Traversal.Admin<?,?>> postStrategyExpectedGlobalChildren;
+
+    /**
+     * Overrides expectedLocalChildren for assertions following strategy 
execution. If left null, expectedLocalChildren is used instead.
+     */
+    @Parameterized.Parameter(value = 5)
+    public List<Traversal.Admin<?,?>> postStrategyExpectedLocalChildren;
+
+    @Parameterized.Parameters(name = "{0}")
+    public static Iterable<Object[]> data() {
+        return Arrays.asList(new Object[][]{
+                {AddVertexStepContract.class,
+                        g.addV("label").property("name", __.constant("cole")),
+                        List.of(),
+                        List.of(__.constant("cole"), new 
ConstantTraversal<>("label")),
+                        null, null
+                },
+                {AddVertexStepContract.class,
+                        g.addV(__.constant("label")).property("name", 
__.constant("cole")),
+                        List.of(),
+                        List.of(__.constant("cole"), __.constant("label")),
+                        null, null
+                },
+                {AddVertexStepContract.class,
+                        g.addV().property("name", 
__.constant("cole")).property(T.label, __.constant("label")).property(T.id, 
__.constant(1)),
+                        List.of(),
+                        List.of(__.constant("cole"), __.constant("label"),  
__.constant(1)),
+                        null, null
+                },
+                {AddVertexStepContract.class,
+                        g.addV(GValue.of("l", "label")).property("name", 
GValue.of("name", "cole")),
+                        List.of(),
+                        List.of(new ConstantTraversal<>("label")), // Property 
is not stored as a child traversal in this case
+                        null, null
+                },
+                {AddVertexStepContract.class,
+                        g.addV("label").property(__.constant("name"), 
__.constant("cole")),
+                        List.of(),
+                        List.of(__.constant("name"), __.constant("cole"), new 
ConstantTraversal<>("label")),
+                        null, null
+                },
+                {AddVertexStepContract.class,
+                        g.inject(1).addV("label").property("name", 
__.constant("cole")),
+                        List.of(),
+                        List.of(__.constant("cole"), new 
ConstantTraversal<>("label")),
+                        null, null
+                },
+                {AddVertexStepContract.class,
+                        
g.inject(1).addV(__.constant("label")).property("name", __.constant("cole")),
+                        List.of(),
+                        List.of(__.constant("cole"), __.constant("label")),
+                        null, null
+                },
+                {AddVertexStepContract.class,
+                        g.inject(1).addV(GValue.of("l", 
"label")).property("name", GValue.of("name", "cole")),
+                        List.of(),
+                        List.of(new ConstantTraversal<>("label")), // Property 
is not stored as a child traversal in this case
+                        null, null
+                },
+                {AddVertexStepContract.class,
+                        
g.inject(1).addV("label").property(__.constant("name"), __.constant("cole")),
+                        List.of(),
+                        List.of(__.constant("name"), __.constant("cole"), new 
ConstantTraversal<>("label")),
+                        null, null
+                },
+                {AddEdgeStepContract.class,
+                        g.addE("label").from(1).to(2).property("name", 
__.constant("cole")),
+                        List.of(),
+                        List.of(__.constant("cole"), new 
ConstantTraversal<>("label"), __.constant(1), __.constant(2)),
+                        null, null
+                },
+                {AddEdgeStepContract.class,
+                        g.addE("label").from(__.V(1)).to(__.V(2))
+                                .property("name", __.constant("cole"))
+                                .property(T.id, __.constant(5)),
+                        List.of(),
+                        List.of(__.constant("cole"), new 
ConstantTraversal<>("label"), __.V(1), __.V(2), __.constant(5)),
+                        null, null
+                },
+                {AddEdgeStepContract.class,
+                        
g.addE("label").from(__.V(1)).to(__.V(2)).property("name", __.constant("cole")),
+                        List.of(),
+                        List.of(__.constant("cole"), new 
ConstantTraversal<>("label"), __.V(1), __.V(2)),
+                        null, null
+                },
+                {AddEdgeStepContract.class,
+                        g.addE(GValue.of("l", "label")).from(GValue.of("from", 
1)).to(GValue.of("to", 2)).property("name", GValue.of("name", "cole")),
+                        List.of(),
+                        List.of(new ConstantTraversal<>("label"), new 
ConstantTraversal(1), new ConstantTraversal(2)),
+                        null, null
+                },
+                {AddEdgeStepContract.class,
+                        
g.addE("label").from(1).to(2).property(__.constant("name"), 
__.constant("cole")),
+                        List.of(),
+                        List.of(__.constant("name"), __.constant("cole"), new 
ConstantTraversal<>("label"), __.constant(1), __.constant(2)),
+                        null, null
+                },
+                {AddEdgeStepContract.class,
+                        
g.inject(1).addE("label").from(1).to(2).property("name", __.constant("cole")),
+                        List.of(),
+                        List.of(__.constant("cole"), new 
ConstantTraversal<>("label"), __.constant(1), __.constant(2)),
+                        null, null
+                },
+                {AddEdgeStepContract.class,
+                        
g.inject(1).addE("label").from(__.V(1)).to(__.V(2)).property("name", 
__.constant("cole")),
+                        List.of(),
+                        List.of(__.constant("cole"), new 
ConstantTraversal<>("label"), __.V(1), __.V(2)),
+                        null, null
+                },
+                {AddEdgeStepContract.class,
+                        g.inject(1).addE(GValue.of("l", 
"label")).from(GValue.of("from", 1)).to(GValue.of("to", 2)).property("name", 
GValue.of("name", "cole")),
+                        List.of(),
+                        List.of(new ConstantTraversal<>("label"), new 
ConstantTraversal(1), new ConstantTraversal(2)),
+                        null, null
+                },
+                {AddEdgeStepContract.class,
+                        
g.inject(1).addE("label").from(1).to(2).property(__.constant("name"), 
__.constant("cole")),
+                        List.of(),
+                        List.of(__.constant("name"), __.constant("cole"), new 
ConstantTraversal<>("label"), __.constant(1), __.constant(2)),
+                        null, null
+                },
+                {CallStepContract.class,
+                        g.call("service"),
+                        List.of(),
+                        List.of(),
+                        null, null
+                },
+                {CallStepContract.class,
+                        g.call("service").with("key", __.constant("value")),
+                        List.of(),
+                        List.of(__.constant("value")),
+                        null, null
+                },
+                {CallStepContract.class,
+                        g.call("service", __.constant(Map.of("key", "value"))),
+                        List.of(),
+                        List.of(__.constant(Map.of("key", "value"))),
+                        null, null
+                },
+                {CallStepContract.class,
+                        g.call("service", __.constant(Map.of("key", 
"value"))).with("key", __.constant("value")),
+                        List.of(),
+                        List.of(__.constant(Map.of("key", "value")), 
__.constant("value")),
+                        null, null
+                },
+                {AddPropertyStepContract.class,
+                        g.inject(1).property("key", "value"),
+                        List.of(),
+                        List.of(new ConstantTraversal<>("value")), // constant 
Value's are internally boxed in Traversals
+                        null, null
+                },
+                {AddPropertyStepContract.class,
+                        g.inject(1).property("key", __.constant("value")),
+                        List.of(),
+                        List.of(__.constant("value")),
+                        null, null
+                },
+                {AddPropertyStepContract.class,
+                        g.inject(1).property(__.constant("key"), 
__.constant("value")),
+                        List.of(),
+                        List.of(__.constant("key"), __.constant("value")),
+                        null, null
+                },
+                {AddPropertyStepContract.class,
+                        g.addV().property("name", "value", "metaKey", 
"metaValue"),
+                        List.of(),
+                        List.of(new ConstantTraversal<>("value")), // constant 
Value's are internally boxed in Traversals
+                        null, null
+                },
+                {AddPropertyStepContract.class,
+                        g.addV().property("name", __.constant("value"), 
"metaKey", __.constant("metaValue")),
+                        List.of(),
+                        List.of(__.constant("value"), 
__.constant("metaValue")),
+                        null, null
+                },
+                {AddPropertyStepContract.class,
+                        g.addV().property(__.constant("name"), 
__.constant("value"), __.constant("metaKey"), __.constant("metaValue")),
+                        List.of(),
+                        List.of(__.constant("name"), __.constant("value"), 
__.constant("metaKey"), __.constant("metaValue")),
+                        null, null
+                },
+                {AddPropertyStepContract.class,
+                        g.addV().property("name", "value", "metaKey1", 
"metaValue1", "metaKey2", "metaValue2"),
+                        List.of(),
+                        List.of(new ConstantTraversal<>("value")), // constant 
Value's are internally boxed in Traversals
+                        null, null
+                },
+                {MergeStepContract.class,
+                        g.mergeV(Map.of("name", "marko")),
+                        List.of(),
+                        List.of(new ConstantTraversal<>(Map.of("name", 
"marko"))), // constant MergeMap's are internally boxed in Traversals
+                        null, null
+                },
+                {MergeStepContract.class,
+                        g.mergeV(__.constant(Map.of("name", "marko"))),
+                        List.of(),
+                        List.of(__.constant(Map.of("name", "marko"))),
+                        null, null
+                },
+                {MergeStepContract.class,
+                        g.mergeV(Map.of("name", 
"marko")).option(Merge.onCreate, __.constant(Map.of("age", 29))),
+                        List.of(),
+                        List.of(new ConstantTraversal<>(Map.of("name", 
"marko")), __.constant(Map.of("age", 29))), // constant MergeMap's are 
internally boxed in Traversals
+                        null, null
+                },
+                {MergeStepContract.class,
+                        g.mergeV(__.constant(Map.of("name", 
"marko"))).option(Merge.onCreate, __.constant(Map.of("age", 
29))).option(Merge.onMatch, __.constant(Map.of("updated", true))),
+                        List.of(),
+                        List.of(__.constant(Map.of("name", "marko")), 
__.constant(Map.of("age", 29)), __.constant(Map.of("updated", true))),
+                        null, null
+                },
+                {MergeStepContract.class,
+                        g.mergeE(Map.of(T.label, "knows")),
+                        List.of(),
+                        List.of(new ConstantTraversal<>(Map.of(T.label, 
"knows"))), // constant MergeMap's are internally boxed in Traversals
+                        null, null
+                },
+                {MergeStepContract.class,
+                        g.mergeE(__.constant(Map.of(T.label, "knows"))),
+                        List.of(),
+                        List.of(__.constant(Map.of(T.label, "knows"))),
+                        null, null
+                },
+                {MergeStepContract.class,
+                        g.mergeE(Map.of(T.label, 
"knows")).option(Merge.onCreate, __.constant(Map.of("weight", 0.5))),
+                        List.of(),
+                        List.of(new ConstantTraversal<>(Map.of(T.label, 
"knows")), __.constant(Map.of("weight", 0.5))), // constant MergeMap's are 
internally boxed in Traversals
+                        null, null
+                },
+                {MergeStepContract.class,
+                        g.mergeE(__.constant(Map.of(T.label, 
"knows"))).option(Merge.onCreate, __.constant(Map.of("weight", 
0.5))).option(Merge.onMatch, __.constant(Map.of("updated", true))),
+                        List.of(),
+                        List.of(__.constant(Map.of(T.label, "knows")), 
__.constant(Map.of("weight", 0.5)), __.constant(Map.of("updated", true))),
+                        null, null
+                },
+                {AggregateGlobalStep.class,
+                        g.V().aggregate("x"),
+                        List.of(),
+                        List.of(),
+                        null, null
+                },
+                {AggregateGlobalStep.class,
+                        g.V().aggregate("x").by("name"),
+                        List.of(),
+                        List.of(new ValueTraversal("name")),
+                        null, null
+                },
+                {AggregateGlobalStep.class,
+                        g.V().aggregate("x").by(__.constant("value")),
+                        List.of(),
+                        List.of(__.constant("value")),
+                        null, null
+                },
+                {AggregateLocalStep.class,
+                        g.V().aggregate(Scope.local, "x"),
+                        List.of(),
+                        List.of(),
+                        null, null
+                },
+                {AggregateLocalStep.class,
+                        g.V().aggregate(Scope.local, "x").by("name"),
+                        List.of(),
+                        List.of(new ValueTraversal("name")),
+                        null, null
+                },
+                {AggregateLocalStep.class,
+                        g.V().aggregate(Scope.local, 
"x").by(__.constant("value")),
+                        List.of(),
+                        List.of(__.constant("value")),
+                        null, null
+                },
+                {AndStep.class,
+                        g.V().and(__.outE(), __.has("age", P.gte(32))),
+                        List.of(),
+                        List.of(__.outE(), __.has("age", P.gte(32))),
+                        null, null
+                },
+                {OrStep.class,
+                        g.V().or(__.outE(), __.has("age", P.gte(32))),
+                        List.of(),
+                        List.of(__.outE(), __.has("age", P.gte(32))),
+                        null, null
+                },
+                {BranchStep.class,
+                        g.V().branch(__.label()).option("person", 
__.values("name")).option("software", __.values("lang")),
+                        List.of(appendComputerAwareEndStep(__.values("name")), 
appendComputerAwareEndStep(__.values("lang"))),
+                        List.of(__.label(), new 
PredicateTraversal<>(P.eq("person")), new 
PredicateTraversal<>(P.eq("software"))), // option keys are wrapped in 
PredicateTraversals internally
+                        null, null
+                },
+                {ChooseStep.class,
+                        g.V().choose(__.out().count()).option(2L, 
__.values("name")).option(3L, __.values("age")),
+                        List.of(appendComputerAwareEndStep(__.values("name")), 
appendComputerAwareEndStep(__.values("age")), 
appendComputerAwareEndStep(__.identity()), 
appendComputerAwareEndStep(__.identity())),
+                        List.of(__.out().count(), new 
PredicateTraversal<>(P.eq(2L)), new PredicateTraversal<>(P.eq(3L))), // option 
keys are wrapped in PredicateTraversals internally
+                        null, List.of(__.outE().count(), new 
PredicateTraversal<>(P.eq(2L)), new PredicateTraversal<>(P.eq(3L)))
+                },
+                {CoalesceStep.class,
+                        g.V().coalesce(__.out("knows"), __.out("created")),
+                        List.of(),
+                        List.of(__.out("knows"), __.out("created")),
+                        null, null
+                },
+                {CombineStep.class,
+                        g.V().fold().combine(__.constant(List.of(1, 2, 3))),
+                        List.of(),
+                        List.of(__.constant(List.of(1, 2, 3))),
+                        null, null
+                },
+                {ConcatStep.class,
+                        g.inject("a", "b").concat(__.constant("c"), 
__.constant("d")),
+                        List.of(),
+                        List.of(__.constant("c"), __.constant("d")),
+                        null, null
+                },
+                {DateDiffStep.class,
+                        
g.inject(OffsetDateTime.parse("1970-01-01T00:00:00.000Z")).dateDiff(__.constant(OffsetDateTime.parse("1970-02-01T00:00:00.000Z"))),
+                        List.of(),
+                        
List.of(__.constant(OffsetDateTime.parse("1970-02-01T00:00:00.000Z"))),
+                        null, null
+                },
+                {DedupGlobalStep.class,
+                        g.V().dedup(),
+                        List.of(),
+                        List.of(),
+                        null, null
+                },
+                {DedupGlobalStep.class,
+                        g.V().dedup().by("name"),
+                        List.of(),
+                        List.of(new ValueTraversal("name")),
+                        null, null
+                },
+                {DedupGlobalStep.class,
+                        g.V().dedup().by(__.constant("value")),
+                        List.of(),
+                        List.of(__.constant("value")),
+                        null, null
+                },
+                {DifferenceStep.class,
+                        g.V().fold().difference(__.constant(List.of(1, 2, 3))),
+                        List.of(),
+                        List.of(__.constant(List.of(1, 2, 3))),
+                        null, null
+                },
+                {DisjunctStep.class,
+                        g.V().fold().disjunct(__.constant(List.of(1, 2, 3))),
+                        List.of(),
+                        List.of(__.constant(List.of(1, 2, 3))),
+                        null, null
+                },
+                {FormatStep.class,
+                        g.V().format("Hello %{name}"),
+                        List.of(),
+                        List.of(),
+                        null, null
+                },
+                {FormatStep.class,
+                        g.V().format("Hello %{name}").by("name"),
+                        List.of(),
+                        List.of(new ValueTraversal("name")),
+                        null, null
+                },
+                {FormatStep.class,
+                        g.V().format("Hello %{name}").by(__.constant("value")),
+                        List.of(),
+                        List.of(__.constant("value")),
+                        null, null
+                },
+                {GroupCountStep.class,
+                        g.V().groupCount(),
+                        List.of(),
+                        List.of(),
+                        null, null
+                },
+                {GroupCountStep.class,
+                        g.V().groupCount().by("name"),
+                        List.of(),
+                        List.of(new ValueTraversal("name")),
+                        null, null
+                },
+                {GroupCountStep.class,
+                        g.V().groupCount().by(__.constant("value")),
+                        List.of(),
+                        List.of(__.constant("value")),
+                        null, null
+                },
+                {GroupCountSideEffectStep.class,
+                        g.V().groupCount("x"),
+                        List.of(),
+                        List.of(),
+                        null, null
+                },
+                {GroupCountSideEffectStep.class,
+                        g.V().groupCount("x").by("name"),
+                        List.of(),
+                        List.of(new ValueTraversal("name")),
+                        null, null
+                },
+                {GroupCountSideEffectStep.class,
+                        g.V().groupCount("x").by(__.constant("value")),
+                        List.of(),
+                        List.of(__.constant("value")),
+                        null, null
+                },
+                {GroupStep.class,
+                        g.V().group(),
+                        List.of(),
+                        List.of(__.fold()),
+                        null, null
+                },
+                {GroupStep.class,
+                        g.V().group().by("name"),
+                        List.of(),
+                        List.of(new ValueTraversal("name"), __.fold()),
+                        null, null
+                },
+                {GroupStep.class,
+                        g.V().group().by("name").by("age"),
+                        List.of(),
+                        List.of(new ValueTraversal("name"), __.map(new 
ValueTraversal("age")).fold()),
+                        null, null
+                },
+                {GroupStep.class,
+                        
g.V().group().by(__.constant("key")).by(__.constant("value")),
+                        List.of(),
+                        List.of(__.constant("key"), __.constant("value")),
+                        null, null
+                },
+                {IntersectStep.class,
+                        g.V().fold().intersect(__.constant(List.of(1, 2, 3))),
+                        List.of(),
+                        List.of(__.constant(List.of(1, 2, 3))),
+                        null, null
+                },
+                {LocalStep.class,
+                        g.V().local(__.outE().count()),
+                        List.of(),
+                        List.of(__.outE().count()),
+                        null, null
+                },
+                {MatchStep.class,
+                        g.V().match(__.as("a").out().as("b"), 
__.as("b").in().as("c")),
+                        List.of(generateMatchChildTraversal("a", "b", 
__.out().asAdmin()), generateMatchChildTraversal("b", "c", __.in().asAdmin())),
+                        List.of(),
+                        null, null
+                },
+                {MathStep.class,
+                        g.V().math("_ + 1"),
+                        List.of(),
+                        List.of(),
+                        null, null
+                },
+                {MathStep.class,
+                        g.V().math("_ + 1").by("age"),
+                        List.of(),
+                        List.of(new ValueTraversal("age")),
+                        null, null
+                },
+                {MathStep.class,
+                        g.V().math("_ + _").by("age").by(__.constant(10)),
+                        List.of(),
+                        List.of(new ValueTraversal("age"), __.constant(10)),
+                        null, null
+                },
+                {MergeStep.class,
+                        g.V().fold().merge(__.constant(List.of(1, 2, 3))),
+                        List.of(),
+                        List.of(__.constant(List.of(1, 2, 3))),
+                        null, null
+                },
+                {NotStep.class,
+                        g.V().not(__.has("age", P.gt(27))),
+                        List.of(),
+                        List.of(__.has("age", P.gt(27))),
+                        null, null
+                },
+                {OptionalStep.class,
+                        g.V().optional(__.out("knows")),
+                        List.of(),
+                        List.of(__.out("knows")),
+                        null, null
+                },
+                {OrderGlobalStep.class,
+                        g.V().order(),
+                        List.of(),
+                        List.of(),
+                        null, null
+                },
+                {OrderGlobalStep.class,
+                        g.V().order().by("name"),
+                        List.of(),
+                        List.of(new ValueTraversal("name")),
+                        null, null
+                },
+                {OrderGlobalStep.class,
+                        g.V().order().by("name").by(__.constant("value")),
+                        List.of(),
+                        List.of(new ValueTraversal("name"), 
__.constant("value")),
+                        null, null
+                },
+                {OrderLocalStep.class,
+                        g.V().fold().order(Scope.local),
+                        List.of(),
+                        List.of(),
+                        null, null
+                },
+                {OrderLocalStep.class,
+                        g.V().fold().order(Scope.local).by("name"),
+                        List.of(),
+                        List.of(new ValueTraversal("name")),
+                        null, null
+                },
+                {OrderLocalStep.class,
+                        
g.V().fold().order(Scope.local).by(__.constant("value")),
+                        List.of(),
+                        List.of(__.constant("value")),
+                        null, null
+                },
+                {PathFilterStep.class,
+                        g.V().simplePath(),
+                        List.of(),
+                        List.of(),
+                        null, null
+                },
+                {PathFilterStep.class,
+                        g.V().cyclicPath(),
+                        List.of(),
+                        List.of(),
+                        null, null
+                },
+                {PathFilterStep.class,
+                        g.V().simplePath().by("name"),
+                        List.of(),
+                        List.of(new ValueTraversal("name")),
+                        null, null
+                },
+                {PathFilterStep.class,
+                        g.V().simplePath().by(__.constant("value")),
+                        List.of(),
+                        List.of(__.constant("value")),
+                        null, null
+                },
+                {PathFilterStep.class,
+                        g.V().cyclicPath().by("age").by(__.constant("value")),
+                        List.of(),
+                        List.of(new ValueTraversal("age"), 
__.constant("value")),
+                        null, null
+                },
+                {PathStep.class,
+                        g.V().path(),
+                        List.of(),
+                        List.of(),
+                        null, null
+                },
+                {PathStep.class,
+                        g.V().out().path().by("age").by("name"),
+                        List.of(),
+                        List.of(new ValueTraversal("age"), new 
ValueTraversal("name")),
+                        null, null
+                },
+                {PathStep.class,
+                        g.V().path().by(__.constant("value")),
+                        List.of(),
+                        List.of(__.constant("value")),
+                        null, null
+                },
+                {ProductStep.class,
+                        g.V().fold().product(__.constant(List.of(1, 2, 3))),
+                        List.of(),
+                        List.of(__.constant(List.of(1, 2, 3))),
+                        null, null
+                },
+                {ProjectStep.class,
+                        g.V().project("a", "b").by("name").by("age"),
+                        List.of(),
+                        List.of(new ValueTraversal("name"), new 
ValueTraversal("age")),
+                        null, null
+                },
+                {ProjectStep.class,
+                        g.V().project("x").by(__.constant("value")),
+                        List.of(),
+                        List.of(__.constant("value")),
+                        null, null
+                },
+                {PropertyMapStep.class,
+                        g.V().valueMap(),
+                        List.of(),
+                        List.of(),
+                        null, null
+                },
+                {PropertyMapStep.class,
+                        g.V().valueMap().by(__.constant("transformed")),
+                        List.of(),
+                        List.of(__.constant("transformed")),
+                        null, null
+                },
+                {RepeatStep.class,
+                        g.V().repeat(__.out()).emit().times(2),
+                        List.of(appendRepeatEndStep(__.out())),
+                        List.of(new LoopTraversal<>(2), 
TrueTraversal.instance()),
+                        null, null
+                },
+                {RepeatStep.class,
+                        g.V().repeat(__.out()).until(__.has("name", "josh")),
+                        List.of(appendRepeatEndStep(__.out())),
+                        List.of(__.has("name", "josh")),
+                        null, null
+                },
+                {RepeatStep.class,
+                        
g.V().repeat(__.out()).emit(__.has("age")).until(__.has("name", "josh")),
+                        List.of(appendRepeatEndStep(__.out())),
+                        List.of(__.has("name", "josh"), __.has("age")),
+                        null, List.of(__.has("name", "josh"), 
__.filter(__.properties("age"))),
+                },
+                {SackValueStep.class,
+                        g.withSack(0).V().sack(Operator.sum),
+                        List.of(),
+                        List.of(),
+                        null, null
+                },
+                {SackValueStep.class,
+                        g.withSack(0).V().sack(Operator.sum).by("age"),
+                        List.of(),
+                        List.of(new ValueTraversal("age")),
+                        null, null
+                },
+                {SackValueStep.class,
+                        
g.withSack(0).V().sack(Operator.sum).by(__.constant("age")),
+                        List.of(),
+                        List.of(__.constant("age")),
+                        null, null
+                },
+                {SampleGlobalStep.class,
+                        g.V().sample(2),
+                        List.of(),
+                        List.of(new ConstantTraversal<>(1.0)),
+                        null, null
+                },
+                {SampleGlobalStep.class,
+                        g.E().sample(2).by("weight"),
+                        List.of(),
+                        List.of(new ValueTraversal("weight")),
+                        null, null
+                },
+                {SampleGlobalStep.class,
+                        g.E().sample(2).by(__.constant("weight")),
+                        List.of(),
+                        List.of(__.constant("weight")),
+                        null, null
+                },
+                {SelectOneStep.class,
+                        g.V().as("a").select("a"),
+                        List.of(),
+                        List.of(),
+                        null, null
+                },
+                {SelectOneStep.class,
+                        g.V().as("a").select("a").by("name"),
+                        List.of(),
+                        List.of(new ValueTraversal("name")),
+                        null, null
+                },
+                {SelectOneStep.class,
+                        g.V().as("a").select("a").by(__.constant("value")),
+                        List.of(),
+                        List.of(__.constant("value")),
+                        null, null
+                },
+                {SelectStep.class,
+                        g.V().as("a").as("b").select("a", "b"),
+                        List.of(),
+                        List.of(),
+                        null, null
+                },
+                {SelectStep.class,
+                        g.V().as("a").as("b").select("a", "b").by("name"),
+                        List.of(),
+                        List.of(new ValueTraversal("name")),
+                        null, null
+                },
+                {SelectStep.class,
+                        g.V().as("a").as("b").select("a", 
"b").by(__.constant("value")),
+                        List.of(),
+                        List.of(__.constant("value")),
+                        null, null
+                },
+                {TraversalSelectStep.class,
+                        g.V().select((Traversal)__.constant("a")),
+                        List.of(),
+                        List.of(__.constant("a")),
+                        null, null
+                },
+                {TraversalSelectStep.class,
+                        g.V().select((Traversal)__.constant("a")).by("name"),
+                        List.of(),
+                        List.of(__.constant("a"), new ValueTraversal("name")),
+                        null, null
+                },
+                {TraversalFilterStep.class,
+                        g.V().filter(__.constant(5)), // a bit of an arbitrary 
case to avoid getting optimized by strategies
+                        List.of(),
+                        List.of(__.constant(5)),
+                        null, null
+                },
+                {TraversalFlatMapStep.class,
+                        g.V().flatMap(__.out()),
+                        List.of(),
+                        List.of(__.out()),
+                        null, null
+                },
+                {TraversalFlatMapStep.class,
+                        g.V().flatMap(__.constant("value")),
+                        List.of(),
+                        List.of(__.constant("value")),
+                        null, null
+                },
+                {TraversalMapStep.class,
+                        g.V().map(__.values("name")),
+                        List.of(),
+                        List.of(__.values("name")),
+                        null, null
+                },
+                {TraversalMapStep.class,
+                        g.V().map(__.constant("value")),
+                        List.of(),
+                        List.of(__.constant("value")),
+                        null, null
+                },
+                {TraversalSideEffectStep.class,
+                        g.V().sideEffect(__.identity()),
+                        List.of(),
+                        List.of(__.identity()),
+                        null, null
+                },
+                {TraversalSideEffectStep.class,
+                        g.V().sideEffect(__.constant("value")),
+                        List.of(),
+                        List.of(__.constant("value")),
+                        null, null
+                },
+                {TreeStep.class,
+                        g.V().out().tree(),
+                        List.of(),
+                        List.of(),
+                        null, null
+                },
+                {TreeStep.class,
+                        g.V().out().tree().by("name"),
+                        List.of(),
+                        List.of(new ValueTraversal("name")),
+                        null, null
+                },
+                {TreeStep.class,
+                        g.V().out().tree().by(__.constant("value")),
+                        List.of(),
+                        List.of(__.constant("value")),
+                        null, null
+                },
+                {TreeSideEffectStep.class,
+                        g.V().out().tree("x"),
+                        List.of(),
+                        List.of(),
+                        null, null
+                },
+                {TreeSideEffectStep.class,
+                        g.V().out().tree("x").by("name"),
+                        List.of(),
+                        List.of(new ValueTraversal("name")),
+                        null, null
+                },
+                {TreeSideEffectStep.class,
+                        g.V().out().tree("x").by(__.constant("value")),
+                        List.of(),
+                        List.of(__.constant("value")),
+                        null, null
+                },
+                {UnionStep.class,
+                        g.union(__.V().values("name"), __.V().values("age")),
+                        
List.of(appendComputerAwareEndStep(__.V().values("name")), 
appendComputerAwareEndStep(__.V().values("age"))),
+                        List.of(new ConstantTraversal<>(Pick.any)),
+                        
List.of(appendComputerAwareEndStep(__.V().values("name").barrier(2500)), 
appendComputerAwareEndStep(__.V().values("age").barrier(2500))),
+                        null
+                },
+                {UnionStep.class,
+                        g.union(__.constant("a"), __.constant("b")),
+                        List.of(appendComputerAwareEndStep(__.constant("a")), 
appendComputerAwareEndStep(__.constant("b"))),
+                        List.of(new ConstantTraversal<>(Pick.any)),
+                        null, null
+                },
+                {WherePredicateStep.class,
+                        g.V().as("a").out().as("b").where("a", P.eq("b")),
+                        List.of(),
+                        List.of(),
+                        null, null
+                },
+                {WherePredicateStep.class,
+                        g.V().as("a").out().as("b").where("a", 
P.eq("b")).by("name"),
+                        List.of(),
+                        List.of(new ValueTraversal("name")),
+                        null, null
+                },
+                {WherePredicateStep.class,
+                        g.V().as("a").out().as("b").where("a", 
P.eq("b")).by(__.constant("value")),
+                        List.of(),
+                        List.of(__.constant("value")),
+                        null, null
+                },
+                {WhereTraversalStep.class,
+                        
g.V().as("a").out().as("b").where(__.as("a").out().as("c")),
+                        List.of(),
+                        List.of(generateWhereChildTraversal("a", "c", 
__.out().asAdmin())),
+                        null, null
+                },
+        });
+    }
+
+    @Test
+    public void doTest() {
+        verifyExpectedParents(expectedGlobalChildren, expectedLocalChildren, 
"(pre-strategy application)");
+
+        traversal = traversal.clone();
+
+        verifyExpectedParents(expectedGlobalChildren, expectedLocalChildren, 
"(cloned traversal, pre-strategy application)");
+
+        
traversal.getStrategies().addStrategies(GValueReductionStrategy.instance());
+        traversal.applyStrategies();
+
+        verifyExpectedParents(postStrategyExpectedGlobalChildren == null ? 
expectedGlobalChildren : postStrategyExpectedGlobalChildren,
+                postStrategyExpectedLocalChildren == null ? 
expectedLocalChildren : postStrategyExpectedLocalChildren,
+                "(pre-strategy application)");
+
+        traversal = traversal.clone();
+
+        verifyExpectedParents(postStrategyExpectedGlobalChildren == null ? 
expectedGlobalChildren : postStrategyExpectedGlobalChildren,
+                postStrategyExpectedLocalChildren == null ? 
expectedLocalChildren : postStrategyExpectedLocalChildren,
+                "(cloned traversal, pre-strategy application)");
+    }
+
+    private void verifyExpectedParents(List<Traversal.Admin<?,?>> 
expectedGlobalChildren, List<Traversal.Admin<?,?>> expectedLocalChildren, 
String messageSuffix) {
+        List<Step> steps = 
TraversalHelper.getStepsOfAssignableClass(stepClass, traversal);
+        assertTrue(String.format("Expected a single step of class %s to test, 
found %d %s", stepClass.getName(), steps.size(), messageSuffix), steps.size() 
== 1);
+        assertTrue(String.format("Expected step to implement TraversalParent 
%s", messageSuffix), steps.get(0) instanceof TraversalParent);
+
+        TraversalParent testStep = (TraversalParent) steps.get(0);
+        assertThat(String.format("getGlobalChildren() did not produce the 
expected results %s", messageSuffix), testStep.getGlobalChildren(), 
containsInAnyOrder(expectedGlobalChildren.toArray()));
+        assertThat(String.format("getLocalChildren() did not produce the 
expected results %s", messageSuffix), testStep.getLocalChildren(), 
containsInAnyOrder(expectedLocalChildren.toArray()));
+
+        for (Traversal.Admin<?, ?> child : testStep.getGlobalChildren()) {
+            if (!(child instanceof AbstractLambdaTraversal)) {
+                // Use reference equality to ensure parent points to the 
correct object. It's not enough that the parents contents match.
+                assertTrue(String.format("Expected child traversal %s to have 
correctly assigned parent %s", child.toString(), messageSuffix), testStep == 
child.getParent());
+            }
+        }
+        for (Traversal.Admin<?, ?> child : testStep.getLocalChildren()) {
+            if (!(child instanceof AbstractLambdaTraversal)) {
+                // Use reference equality to ensure parent points to the 
correct object. It's not enough that the parents contents match.
+                assertTrue(String.format("Expected child traversal %s to have 
correctly assigned parent %s", child.toString(), messageSuffix), testStep == 
child.getParent());
+            }
+        }
+    }
+
+    private static Traversal<?, ?> appendComputerAwareEndStep(final 
Traversal<?, ?> traversal) {
+        traversal.asAdmin().addStep(new 
ComputerAwareStep.EndStep(traversal.asAdmin()));

Review Comment:
   ```suggestion
           traversal.asAdmin().addStep(new 
ComputerAwareStep.EndStep<>(traversal.asAdmin()));
   ```



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