Cram stanza that applies to nothing (#12814)

* test: demonstrate that the cram stanza can apply to nothing

Signed-off-by: Rudi Grinberg <[email protected]>

Author: rgrinberg

test/blackbox-tests/test-cases/cram/cram-applies-to-no-match.t

@@ -0,0 +1,28 @@
+A cram stanza may not match any tests:
+
+  $ cat >dune-project <<EOF
+  > (lang dune 3.21)
+  > EOF
+
+This stanza does not apply to anything:
+
+  $ cat >dune <<EOF
+  > (cram
+  >  (applies_to foobar.t)
+  >  (deps x))
+  > EOF
+
+The user likely meant to write foobar rather than foobar.t
+
+  $ cat >foobar.t <<EOF
+  >   $ echo foo
+  > EOF
+
+Demonstrate that the stanza doesn't apply to anything because this test
+shouldn't even run if it depends on a file x.
+
+  $ dune runtest foobar.t
+  File "foobar.t", line 1, characters 0-0:
+  Error: Files _build/default/foobar.t and _build/default/foobar.t.corrected
+  differ.
+  [1]