trying to find out what I dont understand

makefile

@@ -5,7 +5,7 @@ LDFLAGS := -lcriterion
 
 TESTBIN := /tmp/all_tests
 
-.PHONY: test
+.PHONY: test scratch
 
 run_test: test
 	$(TESTBIN)
@@ -30,3 +30,9 @@ CRITERION_HEADERS := $(shell find /usr/include/criterion)
 ALL_FILES := $(PROJECT_C_FILES) $(CRITERION_HEADERS)
 tags: $(ALL_FILES)
 	ctags -R $(ALL_FILES)
+
+scratch: /tmp/scratch
+	valgrind --leak-check=full --show-leak-kinds=all --error-exitcode=1 /tmp/scratch
+
+/tmp/scratch: scratch.c
+	gcc scratch.c -o /tmp/scratch