fix: update makefile to run only on file changes

.gitignore

@@ -1 +1,3 @@
 .test_sessions
+test/.ran-build-docker
+test/.ran-docker

makefile

@@ -1,20 +1,25 @@
+.PHONY: test
+
 INSTALL_PATH?=/usr/bin/harpoon
+IMAGE_NAME=harpoon-test
 
 install: ./harpoon
 	@install -m 0555 -C ./harpoon $(INSTALL_PATH)
 
 uninstall:
 	@rm $(INSTALL_PATH)
 
-test: docker
-	@docker run -h harpoon-test --name harpoon-test harpoon-test
+test: | test/.ran-build-docker
+	@docker run -h $(IMAGE_NAME) --name $(IMAGE_NAME) $(IMAGE_NAME)
+	@docker rm $(IMAGE_NAME)
 
-docker: test/Dockerfile harpoon test/driver.sh --clean
-	@docker build -t harpoon-test -f test/Dockerfile .
+test/.ran-build-docker: test/Dockerfile harpoon test/driver.sh
+	@$(MAKE) -- --clean >/dev/null
+	@docker build -t $(IMAGE_NAME) -f test/Dockerfile .
+	@touch $@
 
 --clean:
-	@docker ps -a --format '{{.Image}}' | grep -w "harpoon-test" \
+	@docker ps -a --format '{{.Image}}' | grep -w "$(IMAGE_NAME)" \
 		| xargs -I {} docker rm {} >/dev/null 2>&1 || :;
-	@docker images -a --format '{{.Repository}}' | grep -w "harpoon-test" \
+	@docker images -a --format '{{.Repository}}' | grep -w "$(IMAGE_NAME)" \
 		| xargs -I {} docker rmi {} >/dev/null 2>&1 || :;
-