tests: add some script lint checks

There are some common but minor errors we tend to make in
writing test scripts:

  1. Scripts are left non-executable. This is not usually
     noticed immediately because "make test" does not need
     the bit, but it is a matter of git policy to make them
     executable (and is a slight convenience when running
     individual scripts).

  2. Two scripts are allocated the same number. Usually this
     happens on separate branches, and the problem only
     comes about during a merge. But since there is no
     textual conflict, the merger would have to be very
     observant to notice.

     This is also a minor error, but can make GIT_SKIP_TESTS
     ambiguous.

This patch introduces a "test-lint" target which checks
both. It is not invoked by default. You can invoke it as
"make test-lint", or you can make it a prerequisite of
running the tests by specifying "TEST_LINT = test-lint" in
your config.mak or on the command line.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

t/Makefile

@@ -23,10 +23,10 @@ TGITWEB = $(wildcard t95[0-9][0-9]-*.sh)
 
 all: $(DEFAULT_TEST_TARGET)
 
-test: pre-clean
+test: pre-clean $(TEST_LINT)
 	$(MAKE) aggregate-results-and-cleanup
 
-prove: pre-clean
+prove: pre-clean $(TEST_LINT)
 	@echo "*** prove ***"; GIT_CONFIG=.git/config $(PROVE) --exec '$(SHELL_PATH_SQ)' $(GIT_PROVE_OPTS) $(T) :: $(GIT_TEST_OPTS)
 	$(MAKE) clean
 
@@ -41,6 +41,18 @@ clean:
 	$(RM) -r valgrind/bin
 	$(RM) .prove
 
+test-lint: test-lint-duplicates test-lint-executable
+
+test-lint-duplicates:
+	@dups=`echo $(T) | tr ' ' '\n' | sed 's/-.*//' | sort | uniq -d` && \
+		test -z "$$dups" || { \
+		echo >&2 "duplicate test numbers:" $$dups; exit 1; }
+
+test-lint-executable:
+	@bad=`for i in $(T); do test -x "$$i" || echo $$i; done` && \
+		test -z "$$bad" || { \
+		echo >&2 "non-executable tests:" $$bad; exit 1; }
+
 aggregate-results-and-cleanup: $(T)
 	$(MAKE) aggregate-results
 	$(MAKE) clean