add unit testing

makefile

@@ -1,8 +1,11 @@
-default: 1
+default: build day=1
 	# This is my 2021 Advent of Code project
 
 init:
 	mkdir day-$(day); sed 's/#DAY#/$(day)/g' main.go.template | sed 's/#TITLE#/$(title)/g' > day-$(day)/main.go; touch day-$(day)/input.txt
 
-0 1:
-	cd day-$@; go run .
+build:
+	cd day-$(day); go run .
+
+test:
+	cd day-$(day); go test