Fix the test merged in the previous commit

plugins/ct.mk

@@ -41,10 +41,13 @@ CT_RUN = ct_run \
 ifeq ($(CT_SUITES),)
 ct: $(if $(IS_APP),,apps-ct)
 else
+# We do not run tests if we are in an apps/* with no test directory.
+ifneq ($(IS_APP)$(wildcard $(TEST_DIR)),1)
 ct: test-build $(if $(IS_APP),,apps-ct)
 	$(verbose) mkdir -p $(CT_LOGS_DIR)
 	$(gen_verbose) $(CT_RUN) -sname ct_$(PROJECT) -suite $(addsuffix _SUITE,$(CT_SUITES)) $(CT_OPTS)
 endif
+endif
 
 ifneq ($(ALL_APPS_DIRS),)
 define ct_app_target

test/plugin_ct.mk

@@ -76,7 +76,10 @@ ct-apps: build clean
 		"call_my_lib(_) -> 4 = my_lib:random_int()." > $(APP)/test/my_root_SUITE.erl
 
 	$i "Check that Common Test runs tests"
-	$t $(MAKE) -C $(APP) ct $v CT_SUITES=my_root
+	$t $(MAKE) -C $(APP) ct $v
+
+	$i "Check that Common Test runs tests from a specific test suite"
+	$t $(MAKE) -C $(APP) ct CT_SUITES=my_root $v
 
 ct-apps-only: build clean