test(image): cover docker tag validation

pkg/image/image_test.go

@@ -2,6 +2,7 @@ package image
 
 import (
 	"sort"
+	"strings"
 	"testing"
 
 	"github.com/google/go-containerregistry/pkg/name"
@@ -62,3 +63,73 @@ func TestParseReference_DoesNotSpecialCaseDockerInternalHost(t *testing.T) {
 		)
 	}
 }
+
+func TestIsValidDockerTag(t *testing.T) {
+	longTag := strings.Repeat("a", DockerTagMaxSize)
+	overlongTag := strings.Repeat("a", DockerTagMaxSize+1)
+	const latestTag = "latest"
+
+	tests := []struct {
+		name string
+		tag  string
+		want bool
+	}{
+		{"empty accepted as no-tag sentinel", "", true},
+		{"single char", "a", true},
+		{latestTag, latestTag, true},
+		{"semver", "v1.0.0", true},
+		{"numeric", "3.18", true},
+		{"dotted and hyphenated", "ubuntu-20.04", true},
+		{"underscore", "a_b", true},
+		{"at max size", longTag, true},
+		{"leading dot", ".latest", false},
+		{"leading hyphen", "-v1", false},
+		{"slash", "foo/bar", false},
+		{"colon", "v1:0", false},
+		{"space", "tag with space", false},
+		{"at sign", "tag@2", false},
+		{"non-ascii", "α", false},
+		{"over max size", overlongTag, false},
+	}
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := IsValidDockerTag(tc.tag); got != tc.want {
+				t.Errorf("IsValidDockerTag(%q) = %v, want %v", tc.tag, got, tc.want)
+			}
+		})
+	}
+}
+
+func TestValidateTags(t *testing.T) {
+	t.Run("all valid", func(t *testing.T) {
+		if err := ValidateTags([]string{"latest", "v1.0.0", "3.18"}); err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+	})
+
+	t.Run("empty slice", func(t *testing.T) {
+		if err := ValidateTags(nil); err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+	})
+
+	t.Run("rejects invalid tag with offending value in message", func(t *testing.T) {
+		err := ValidateTags([]string{"latest", "foo/bar"})
+		if err == nil {
+			t.Fatal("expected error for invalid tag, got nil")
+		}
+		if !strings.Contains(err.Error(), `"foo/bar"`) {
+			t.Errorf("expected error to quote the offending tag %q, got: %v", "foo/bar", err)
+		}
+	})
+
+	t.Run("reports first invalid tag", func(t *testing.T) {
+		err := ValidateTags([]string{".bad", "-also-bad"})
+		if err == nil {
+			t.Fatal("expected error for invalid tag, got nil")
+		}
+		if !strings.Contains(err.Error(), `".bad"`) {
+			t.Errorf("expected first invalid tag in error, got: %v", err)
+		}
+	})
+}