Fix issue with running test on windows w/no-parallel

Tests/BasicsTests/AsyncProcessTests.swift

@@ -20,7 +20,6 @@ import struct TSCBasic.ByteString
 import struct TSCBasic.Format
 import class TSCBasic.Thread
 import func TSCBasic.withTemporaryFile
-import func TSCTestSupport.withCustomEnv
 
 #if os(Windows)
 let catExecutable = "type"
@@ -168,7 +167,7 @@ final class AsyncProcessTests: XCTestCase {
             #endif
             try localFileSystem.writeFileContents(tempExecutable, bytes: exitScriptContent)
 
-            try withCustomEnv(["PATH": tmpdir.pathString]) {
+            try Environment.makeCustom(["PATH": tmpdir.pathString]) {
                 XCTAssertEqual(AsyncProcess.findExecutable("nonExecutableProgram"), nil)
             }
         }
@@ -184,7 +183,7 @@ final class AsyncProcessTests: XCTestCase {
 
             """)
 
-            try withCustomEnv(["PATH": tmpdir.pathString]) {
+            try Environment.makeCustom(["PATH": tmpdir.pathString]) {
                 do {
                     let process = AsyncProcess(args: "nonExecutableProgram")
                     try process.launch()

Tests/BasicsTests/Environment/EnvironmentTests.swift

@@ -16,6 +16,7 @@ import Foundation
 import Basics
 
 import Testing
+import _InternalTestSupport
 
 struct EnvironmentTests {
     @Test
@@ -144,6 +145,20 @@ struct EnvironmentTests {
         #expect(Environment.current[key] == nil)
     }
 
+    /// Important: This test is inherently race-prone, if it is proven to be
+    /// flaky, it should run in a singled threaded environment/removed entirely.
+    @Test
+    func makeCustomPathEnv() async throws {
+        try XCTSkipOnWindows(because: "Fails in CI due to parallel running tests", skipPlatformCi: true, skipSelfHostedCI: true)
+        let customEnvironment: Environment = .current
+        let origPath = customEnvironment[.path]
+
+        try Environment.makeCustom(["PATH": "/foo/bar"]) {
+            #expect(Environment.current[.path] == "/foo/bar")
+        }
+        #expect(Environment.current[.path] == origPath)
+    }
+
     /// Important: This test is inherently race-prone, if it is proven to be
     /// flaky, it should run in a singled threaded environment/removed entirely.
     @Test

Tests/FunctionalTests/TraitTests.swift

@@ -328,8 +328,7 @@ final class TraitTests: XCTestCase {
                         error: Disabled default traits by package 'disablingemptydefaultsexample' on package 'Package11' that declares no traits. This is prohibited to allow packages to adopt traits initially without causing an API break.
 
                         """
-                XCTAssertTrue(stderr.contains(expectedErr))
-
+                XCTAssertMatch(stderr, .contains(expectedErr))
             }
         }
     }