Hello! Just a note that I've been meaning to send for some time.
"Michael Gran" <spk...@yahoo.com> writes: > http://git.savannah.gnu.org/cgit/guile.git/commit/?id=9b0c25f6d18d5be318ea3a47fd87cf7e63b689e1 [...] > --- a/test-suite/tests/strings.test > +++ b/test-suite/tests/strings.test [...] > +;; > +;; string internals > +;; > + > +;; Some abbreviations > +;; BMP - Basic Multilingual Plane (codepoints below U+FFFF) > +;; SMP - Suplementary Multilingual Plane (codebpoints from U+10000 to > U+1FFFF) > + > +(with-test-prefix "string internals" > + > + (pass-if "new string starts at 1st char in stringbuf" > + (let ((s "abc")) > + (= 0 (assq-ref (%string-dump s) 'start)))) > + > + (pass-if "length of new string same as stringbuf" > + (let ((s "def")) > + (= (string-length s) (assq-ref (%string-dump s) 'stringbuf-length)))) > + > + (pass-if "contents of new string same as stringbuf" > + (let ((s "ghi")) > + (string=? s (assq-ref (%string-dump s) 'stringbuf-chars)))) > + > + (pass-if "writable strings are not read-only" > + (let ((s "zyx")) > + (not (assq-ref (%string-dump s) 'read-only)))) > + > + (pass-if "read-only strings are read-only" > + (let ((s (substring/read-only "zyx" 0))) > + (assq-ref (%string-dump s) 'read-only))) > + > + (pass-if "null strings are inlined" > + (let ((s "")) > + (assq-ref (%string-dump s) 'stringbuf-inline))) First of all, thanks for taking the time to write unit tests! I'm not fully convinced by some of these "string internals" tests, though. These are "white box tests". I believe these tests are mostly useful when written by someone different than the one who implemented the code under test, both of whom following a given specification. When someone writes both the code and the white box tests, I'm afraid they end up writing the same code twice, just differently. For example: SCM scm_i_substring_read_only (SCM str, size_t start, size_t end) { [...] return scm_double_cell (RO_STRING_TAG, /* <--- read-only */ SCM_UNPACK(buf), (scm_t_bits)str_start + start, (scm_t_bits) end - start); } and: (pass-if "read-only strings are read-only" (let ((s (substring/read-only "zyx" 0))) (assq-ref (%string-dump s) 'read-only))) Thus, I think such tests don't provide much information. Conversely, for this example, a black-box test of the public API would have helped catch regressions and non-conformance issues: (pass-if-exception exception:read-only-string (string-set! (substring/read-only "zyx" 0) 1 #\x)) Another issue is that these tests expose a lot of the implementation details, e.g.: (pass-if "short Latin-1 encoded strings are inlined" (let ((s "m")) (assq-ref (%string-dump s) 'stringbuf-inline))) The inline/outline distinction is an implementation detail. If we change it (that's something we could get rid of in the BDW-GC branch, for instance) then the tests will have to be rewritten or removed. Conversely, black box tests can give confidence that a change in implementation details did have any user-visible impact. There *are* situations where the gap between the public API and the internals is too important, and white box tests can come in handy here (that's why `%string-dump' et al. are nice tools). However, often, I think it's better to have good coverage of the public API than a wealth of "obvious" white-box tests. What do you think? Thanks, Ludo'.
