avoid rebuilding dfmt unnecessarily for test

makefile

@@ -10,12 +10,14 @@ LDC_FLAGS := -g -w -oq $(INCLUDE_PATHS)
 dmd: bin/dfmt
 
 ldc: $(SRC)
-	ldc2 $(LDC_FLAGS) $(SRC) -ofbin/dfmt
+	ldc2 $(LDC_FLAGS) $^ -ofbin/dfmt
 	-rm -f *.o
 
-test:
-	dmd $(DMD_TEST_FLAGS) $(SRC) -ofbin/dfmt
+test: bin/dfmt-test
 	cd tests && ./test.sh
 
+bin/dfmt-test: $(SRC)
+	dmd $(DMD_TEST_FLAGS) $^ -of$@
+
 bin/dfmt: $(SRC)
-	dmd $(DMD_FLAGS) $(SRC) -ofbin/dfmt
+	dmd $(DMD_FLAGS) $^ -of$@

tests/test.sh

@@ -12,7 +12,7 @@ do
 		else
 			args=
 		fi
-		../bin/dfmt --brace_style=${braceStyle} ${args} "${source}" > "${braceStyle}/${source}.out"
+		../bin/dfmt-test --brace_style=${braceStyle} ${args} "${source}" > "${braceStyle}/${source}.out"
 		diff -u "${braceStyle}/${source}.ref" "${braceStyle}/${source}.out"
 	done
 done