[test-improver] Improve tests for version.BuildVersionString

internal/version/version.go

@@ -10,6 +10,10 @@ import (
 
 var logVersion = logger.New("version:version")
 
+// readBuildInfo is a package-level variable wrapping debug.ReadBuildInfo to
+// allow test injection without changing the public API.
+var readBuildInfo = debug.ReadBuildInfo
+
 const shortHashLength = 7
 
 // vcsCommitFromBuildInfo extracts the vcs.revision setting from build info,
@@ -88,15 +92,15 @@ func BuildVersionString(mainVersion, gitCommit, buildDate string) string {
 
 	if gitCommit != "" {
 		parts = append(parts, fmt.Sprintf("commit: %s", gitCommit))
-	} else if buildInfo, ok := debug.ReadBuildInfo(); ok {
+	} else if buildInfo, ok := readBuildInfo(); ok {
 		if commit := vcsCommitFromBuildInfo(buildInfo); commit != "" {
 			parts = append(parts, fmt.Sprintf("commit: %s", commit))
 		}
 	}
 
 	if buildDate != "" {
 		parts = append(parts, fmt.Sprintf("built: %s", buildDate))
-	} else if buildInfo, ok := debug.ReadBuildInfo(); ok {
+	} else if buildInfo, ok := readBuildInfo(); ok {
 		if date := vcsTimeFromBuildInfo(buildInfo); date != "" {
 			parts = append(parts, fmt.Sprintf("built: %s", date))
 		}

internal/version/version_test.go

@@ -152,6 +152,49 @@ func makeTestBuildInfo(settings map[string]string) *debug.BuildInfo {
 	return info
 }
 
+func TestBuildVersionString_FallbackFromBuildInfo(t *testing.T) {
+	origReadBuildInfo := readBuildInfo
+	t.Cleanup(func() { readBuildInfo = origReadBuildInfo })
+
+	mockInfo := makeTestBuildInfo(map[string]string{
+		"vcs.revision": "abcdef1234567890abcdef12",
+		"vcs.time":     "2024-06-01T12:00:00Z",
+	})
+	readBuildInfo = func() (*debug.BuildInfo, bool) {
+		return mockInfo, true
+	}
+
+	t.Run("uses truncated vcs.revision when gitCommit is empty", func(t *testing.T) {
+		got := BuildVersionString("v1.0.0", "", "2024-01-01")
+		assert.Contains(t, got, "commit: abcdef1", "should include truncated commit from build info")
+		assert.Contains(t, got, "built: 2024-01-01", "should use explicit buildDate")
+	})
+
+	t.Run("uses vcs.time when buildDate is empty", func(t *testing.T) {
+		got := BuildVersionString("v1.0.0", "explicit", "")
+		assert.Contains(t, got, "commit: explicit", "should use explicit gitCommit")
+		assert.Contains(t, got, "built: 2024-06-01T12:00:00Z", "should include vcs.time from build info")
+	})
+
+	t.Run("uses both vcs fields when gitCommit and buildDate are empty", func(t *testing.T) {
+		got := BuildVersionString("v1.0.0", "", "")
+		assert.Equal(t, "v1.0.0, commit: abcdef1, built: 2024-06-01T12:00:00Z", got)
+	})
+
+	t.Run("build info unavailable leaves commit and date absent", func(t *testing.T) {
+		readBuildInfo = func() (*debug.BuildInfo, bool) { return nil, false }
+		got := BuildVersionString("v1.0.0", "", "")
+		assert.Equal(t, "v1.0.0", got, "no fallback data when build info is unavailable")
+	})
+
+	t.Run("build info available but no vcs settings", func(t *testing.T) {
+		emptyInfo := makeTestBuildInfo(map[string]string{})
+		readBuildInfo = func() (*debug.BuildInfo, bool) { return emptyInfo, true }
+		got := BuildVersionString("v2.0.0", "", "")
+		assert.Equal(t, "v2.0.0", got, "no commit or date appended when vcs settings absent")
+	})
+}
+
 func TestVCSCommitFromBuildInfo(t *testing.T) {
 	tests := []struct {
 		name      string