chore: import upstream snapshot with attribution

Tests/ContainerResourceTests/ResourceLabelsTest.swift

@@ -0,0 +1,50 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2026 Apple Inc. and the container project authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//===----------------------------------------------------------------------===//
+
+import Testing
+
+@testable import ContainerResource
+
+struct ResourceLabelsTest {
+    @Test func testValidationGoodLabels() throws {
+        let allLabels: [[String: String]] = [
+            ["com.example.my-label": "bar"],
+            ["mycompany.com/my-label": "bar"],
+            ["foo": String(repeating: "0", count: 4096 - "foo".count - "=".count)],
+            [String(repeating: "0", count: 128): ""],
+        ]
+        for labels in allLabels {
+            _ = try ResourceLabels(labels)
+        }
+    }
+
+    @Test func testValidationBadLabels() throws {
+        let allLabels: [[String: String]] = [
+            [String(repeating: "0", count: 129): ""],
+            ["foo": String(repeating: "0", count: 4097 - "foo".count - "=".count)],
+            ["com..example.my-label": "bar"],
+            ["mycompany.com//my-label": "bar"],
+            ["": String(repeating: "0", count: 4096 - "foo".count - "=".count)],
+        ]
+        for labels in allLabels {
+            #expect {
+                _ = try ResourceLabels(labels)
+            } throws: { error in
+                error is ResourceLabels.LabelError
+            }
+        }
+    }
+}