Enforce tests do not change files in source tree (#9625)

.drone.yml

@@ -118,7 +118,7 @@ steps:
     pull: always
     image: golang:1.13
     commands:
-      - make unit-test-coverage
+      - make unit-test-coverage test-check
     environment:
       GOPROXY: off
       TAGS: bindata sqlite sqlite_unlock_notify

Makefile

@@ -226,6 +226,18 @@ fmt-check:
 test:
 	GO111MODULE=on $(GO) test -mod=vendor -tags='sqlite sqlite_unlock_notify' $(PACKAGES)
 
+PHONY: test-check
+test-check:
+	@echo "Checking if tests have changed the source tree...";
+	@diff=$$(git status -s); \
+	if [ -n "$$diff" ]; then \
+		echo "make test has changed files in the source tree:"; \
+		echo "$${diff}"; \
+		echo "You should change the tests to create these files in a temporary directory."; \
+		echo "Do not simply add these files to .gitignore"; \
+		exit 1; \
+	fi;
+
 .PHONY: test\#%
 test\#%:
 	GO111MODULE=on $(GO) test -mod=vendor -tags='sqlite sqlite_unlock_notify' -run $* $(PACKAGES)