only rebuild test executable if idr files change. restore test config…

… after tests run

test/Makefile

@@ -6,10 +6,16 @@ harmony ?= $(shell realpath "${PWD}/../harmony")
 
 INTERACTIVE ?= "--interactive"
 
+IDR_SOURCES := $(wildcard *.idr)
+
+build/exec/test: $(IDR_SOURCES)
+	idris2 --build harmony-tests.ipkg
+
 export harmony
-test:
-	idris2 --build harmony-tests.ipkg && \
-	./build/exec/test runtests $(INTERACTIVE)
+test: build/exec/test
+	cp config-command/harmony.json harmony.json.bak && \
+	  build/exec/test runtests $(INTERACTIVE) && \
+	  mv harmony.json.bak config-command/harmony.json
 
 clean:
 	rm -rf ./test/build