Fix issue with running test on windows w/no-parallel (#8676)

The AsyncProcess Tests were using a TSCTestSupport method to temporarily
change the PATH env but seems to have a bug where it removes the
variable instead of restoring resulting in any future test needing PATH
to fail. This switches it to using the similar method that is in SwiftPM
Environment.swift

Author: daveinglis

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 +145,19 @@ 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(.disabled(if: isInCiEnvironment, "This test can disrupt other tests running in parallel."))
+    func makeCustomPathEnv() async throws {
+        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/CommandsTests/RunCommandTests.swift

@@ -142,8 +142,8 @@ class RunCommandTestCase: CommandsBuildProviderTestCase {
     }
 
     func testSwiftRunSIGINT() throws {
-        try XCTSkipIfPlatformCI()
-        try XCTSkipOnWindows(because: "fails due to possible timing issues, need investigation")
+        try XCTSkipIfPlatformCI(because: "This seems to be flaky in CI")
+        try XCTSkipIfselfHostedCI(because: "This seems to be flaky in CI")
         try fixture(name: "Miscellaneous/SwiftRun") { fixturePath in
             let mainFilePath = fixturePath.appending("main.swift")
             try localFileSystem.removeFileTree(mainFilePath)

Tests/FunctionalTests/PluginTests.swift

@@ -665,6 +665,8 @@ final class PluginTests: XCTestCase {
     }
 
     func testCommandPluginCancellation() async throws {
+        try XCTSkipOnWindows(because: "This hangs intermittently on windows in CI", skipSelfHostedCI: true)
+
         // Only run the test if the environment in which we're running actually supports Swift concurrency (which the plugin APIs require).
         try XCTSkipIf(!UserToolchain.default.supportsSwiftConcurrency(), "skipping because test environment doesn't support concurrency")
 

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))
             }
         }
     }