Add a workaround to allow querying the test program for '--help'

without requiring test data. The issue was raised at
mirage/alcotest#358

semgrep-core/Makefile

@@ -36,6 +36,9 @@ clean:
 #
 .PHONY: test
 test: all
+	# ensure that '--help' is available and that we don't load test data
+	# until the tests need to run.
+	./_build/default/tests/test.exe --help 2>&1 >/dev/null
 	$(MAKE) -C src/spacegrep test
 	dune runtest -f --no-buffer
 

semgrep-core/tests/Test.ml

@@ -74,8 +74,17 @@ let tests () = List.flatten [
 (* Entry point *)
 (*****************************************************************************)
 
+(*
+   This allows running the test program with '--help' from any folder
+   without getting an error due to not being able to load test data.
+*)
+let tests_with_delayed_error () =
+  try tests ()
+  with e ->
+     ["cannot load test data - not a real test", (fun () -> raise e)]
+
 let main () =
-  let alcotest_tests = Testutil.to_alcotest (tests ()) in
+  let alcotest_tests = Testutil.to_alcotest (tests_with_delayed_error ()) in
   Alcotest.run "semgrep-core" alcotest_tests
 
 let () = main ()