diff --git a/pkg/id/id_test.go b/pkg/id/id_test.go
new file mode 100644
index 0000000000..2013913987
--- /dev/null
+++ b/pkg/id/id_test.go
@@ -0,0 +1,113 @@
+package id
+
+import (
+	"strings"
+	"testing"
+)
+
+const (
+	fooVal = "foo"
+	barVal = "bar"
+)
+
+func TestSafeConcatName(t *testing.T) {
+	tests := []struct {
+		name string
+		in   []string
+		want string
+	}{
+		{"single", []string{fooVal}, fooVal},
+		{"multiple", []string{fooVal, barVal, "baz"}, "foo-bar-baz"},
+		{"empty parts joined", []string{"", barVal}, "-bar"},
+	}
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := SafeConcatName(tc.in...); got != tc.want {
+				t.Fatalf("SafeConcatName(%v) = %q, want %q", tc.in, got, tc.want)
+			}
+		})
+	}
+}
+
+func TestSafeConcatNameMaxUnderLimit(t *testing.T) {
+	got := SafeConcatNameMax([]string{fooVal, barVal}, 63)
+	if got != "foo-bar" {
+		t.Fatalf("SafeConcatNameMax = %q, want %q", got, "foo-bar")
+	}
+}
+
+func TestSafeConcatNameMaxExactLimit(t *testing.T) {
+	input := strings.Repeat("a", 63)
+	got := SafeConcatNameMax([]string{input}, 63)
+	if len(got) != 63 {
+		t.Fatalf("length = %d, want 63 (got %q)", len(got), got)
+	}
+	if got != input {
+		t.Fatalf("SafeConcatNameMax at limit = %q, want %q", got, input)
+	}
+}
+
+func TestSafeConcatNameMaxOverLimit(t *testing.T) {
+	const maxLen = 63
+	input := strings.Repeat("a", 100)
+	got := SafeConcatNameMax([]string{input}, maxLen)
+	if len(got) != maxLen {
+		t.Fatalf("length = %d, want %d (got %q)", len(got), maxLen, got)
+	}
+	if got[maxLen-8] != '-' {
+		t.Fatalf("expected hash separator at index %d, got %q", maxLen-8, got)
+	}
+	if got[:maxLen-8] != input[:maxLen-8] {
+		t.Fatalf("prefix not preserved: %q", got)
+	}
+}
+
+func TestSafeConcatNameMaxStripsTrailingDot(t *testing.T) {
+	const maxLen = 63
+	input := "a." + strings.Repeat("b", maxLen)
+	got := SafeConcatNameMax([]string{input}, maxLen)
+	if len(got) != maxLen {
+		t.Fatalf("length = %d, want %d (got %q)", len(got), maxLen, got)
+	}
+	if strings.Contains(got, ".-") {
+		t.Fatalf("expected trailing dot stripped, got %q", got)
+	}
+}
+
+func TestSafeConcatNameMaxIsDeterministic(t *testing.T) {
+	input := strings.Repeat("x", 100)
+	first := SafeConcatNameMax([]string{input}, 63)
+	second := SafeConcatNameMax([]string{input}, 63)
+	if first != second {
+		t.Fatalf("not deterministic: %q != %q", first, second)
+	}
+}
+
+func TestToDockerImageName(t *testing.T) {
+	tests := []struct {
+		name string
+		in   string
+		want string
+	}{
+		{"lowercases", "MyImage", "myimage"},
+		{"strips invalid chars", "my.image:tag@special!", "myimagetagspecial"},
+		{"keeps allowed separators", "my_image-name", "my_image-name"},
+		{"empty stays empty", "", ""},
+	}
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := ToDockerImageName(tc.in); got != tc.want {
+				t.Fatalf("ToDockerImageName(%q) = %q, want %q", tc.in, got, tc.want)
+			}
+		})
+	}
+}
+
+func TestToDockerImageNameOnlyLowercase(t *testing.T) {
+	got := ToDockerImageName("ABC123")
+	for _, r := range got {
+		if r >= 'A' && r <= 'Z' {
+			t.Fatalf("result contains uppercase rune %q in %q", r, got)
+		}
+	}
+}