Add tests target to Makefile

Makefile

@@ -1,11 +1,15 @@
-.PHONY: all build clean fmt
+.PHONY: all build clean fmt tests
 
-all: fmt build
+all: clean fmt tests build
 
 fmt:
 	@echo 'Reformat Go code ...'
 	find . -type f -name '*.go' -exec go fmt {} \;
 
+tests:
+	@echo 'Run all tests ...'
+	go test ./...
+
 build:
 	@echo 'Build seiso binary ...'
 	go build