Add execTime tests

.github/workflows/build.yml

@@ -13,4 +13,5 @@ jobs:
         with:
           go-version: '1.21'
       - run: test -z $(gofmt -l .)
+      - run: go test ./...
       - run: go build ./cmd/gokart.go

internal/execTime_test.go

@@ -0,0 +1,18 @@
+package internal
+
+import "testing"
+
+func TestFormatMinutesSeconds(t *testing.T) {
+	cases := map[float64]string{
+		3.14:   "3.1s",
+		60:     "1m 0.0s",
+		3712.5: "61m 52.5s",
+	}
+
+	for in, expected := range cases {
+		actual := formatMinutesSeconds(in)
+		if actual != expected {
+			t.Errorf("formatMinutesSeconds(%f) = %s, expected %s", in, actual, expected)
+		}
+	}
+}