chore: import upstream snapshot with attribution

Tests/ContainerizationTests/DNSTests.swift

@@ -0,0 +1,84 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2025-2026 Apple Inc. and the Containerization 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 Foundation
+import Testing
+
+@testable import Containerization
+
+struct DNSTests {
+
+    @Test func dnsResolvConfWithAllFields() {
+        let dns = DNS(
+            nameservers: ["8.8.8.8", "1.1.1.1"],
+            domain: "example.com",
+            searchDomains: ["internal.com", "test.com"],
+            options: ["ndots:2", "timeout:1"]
+        )
+
+        let expected = "nameserver 8.8.8.8\nnameserver 1.1.1.1\ndomain example.com\nsearch internal.com test.com\noptions ndots:2 timeout:1\n"
+        #expect(dns.resolvConf == expected)
+    }
+
+    @Test func dnsResolvConfWithEmptyFields() {
+        let dns = DNS(
+            nameservers: [],
+            domain: nil,
+            searchDomains: [],
+            options: []
+        )
+
+        // Should return empty string when all fields are empty
+        #expect(dns.resolvConf == "")
+    }
+
+    @Test func dnsResolvConfWithOnlyNameservers() {
+        let dns = DNS(nameservers: ["8.8.8.8"])
+
+        let expected = "nameserver 8.8.8.8\n"
+        #expect(dns.resolvConf == expected)
+    }
+
+    @Test func dnsValidateAcceptsValidIPv4Nameservers() throws {
+        let dns = DNS(nameservers: ["8.8.8.8", "1.1.1.1"])
+        #expect(throws: Never.self) { try dns.validate() }
+    }
+
+    @Test func dnsValidateAcceptsValidIPv6Nameservers() throws {
+        let dns = DNS(nameservers: ["2001:4860:4860::8888", "::1"])
+        #expect(throws: Never.self) { try dns.validate() }
+    }
+
+    @Test func dnsValidateAcceptsMixedIPv4AndIPv6Nameservers() throws {
+        let dns = DNS(nameservers: ["8.8.8.8", "2001:4860:4860::8844"])
+        #expect(throws: Never.self) { try dns.validate() }
+    }
+
+    @Test func dnsValidateAcceptsEmptyNameservers() throws {
+        let dns = DNS(nameservers: [])
+        #expect(throws: Never.self) { try dns.validate() }
+    }
+
+    @Test func dnsValidateRejectsHostname() {
+        let dns = DNS(nameservers: ["dns.example.com"])
+        #expect(throws: (any Error).self) { try dns.validate() }
+    }
+
+    @Test func dnsValidateRejectsInvalidAddress() {
+        let dns = DNS(nameservers: ["not-an-ip"])
+        #expect(throws: (any Error).self) { try dns.validate() }
+    }
+}