fix testability

Author: haya14busa

main.go

@@ -48,15 +48,23 @@ func run(w io.Writer) error {
 	if len(tags) == 0 {
 		return errors.New("existing tag not found")
 	}
-	latest, err := semver.NewVersion(latestSemVer(tags))
+	next, err := nextTag(tags, bumpLevel(flag.Args()))
 	if err != nil {
 		return err
 	}
-	next := nextSemVer(latest, bumpLevel(flag.Args()))
-	fmt.Fprintln(w, next.Original())
+	fmt.Fprintln(w, next)
 	return nil
 }
 
+func nextTag(tags []string, level Level) (string, error) {
+	latest, err := semver.NewVersion(latestSemVer(tags))
+	if err != nil {
+		return "", err
+	}
+	next := nextSemVer(latest, level)
+	return next.Original(), nil
+}
+
 func tags(ctx context.Context) ([]string, error) {
 	cmd := exec.CommandContext(ctx, "git", "tag")
 	b, err := cmd.CombinedOutput()

main_test.go

@@ -1,14 +1,15 @@
 package main
 
 import (
-	"bytes"
 	"testing"
 )
 
-func TestRun(t *testing.T) {
-	stdout := new(bytes.Buffer)
-	run(stdout)
-	if stdout.String() == "" {
-		t.Error("got empty result")
+func TestNextTag(t *testing.T) {
+	got, err := nextTag([]string{"v1.0.1", "v1.11.0"}, PATCH)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if want := "v1.11.1"; got != want {
+		t.Errorf("nextTag({v1.0.1, v1.11.0}, PATCH) = %v, want %v", got, want)
 	}
 }