add sub function

main.go

@@ -27,6 +27,11 @@ func main() {
 		b, _ := strconv.Atoi(r.URL.Query().Get("b"))
 		json.NewEncoder(w).Encode(map[string]int{"result": sum(a, b)})
 	})
+	mux.HandleFunc("/sub", func(w http.ResponseWriter, r *http.Request) {
+		a, _ := strconv.Atoi(r.URL.Query().Get("a"))
+		b, _ := strconv.Atoi(r.URL.Query().Get("b"))
+		json.NewEncoder(w).Encode(map[string]int{"result": sub(a, b)})
+	})
 
 	http.ListenAndServe(":8080", mux)
 }
@@ -34,3 +39,7 @@ func main() {
 func sum(a, b int) int {
 	return a + b
 }
+
+func sub(a, b int) int {
+	return a - b
+}

main_test.go

@@ -20,3 +20,20 @@ func Test_sum(t *testing.T) {
 		}
 	}
 }
+
+func Test_sub(t *testing.T) {
+	tests := []struct {
+		a, b int
+		want int
+	}{
+		{1, 2, -1},
+		{-1, 1, -2},
+		{0, 0, 0},
+	}
+
+	for _, test := range tests {
+		if got := sub(test.a, test.b); got != test.want {
+			t.Errorf("sub(%d, %d) = %d, want %d", test.a, test.b, got, test.want)
+		}
+	}
+}