Fix a unit test that is writing to the checkout of SwiftPM itself.

This was never a good thing to do, but now that we have v2 of Package.resolved, it is an actively harmful thing to do if the IDE or toolchain being used to build SwiftPM and run the tests is older (e.g. using the 5.5 toolchain but working on main).

There's not need at all to run this test against SwiftPM itself — a sample package created for the purpose in the usual temporary directory is all that's needed.

rdar://83222890

Author: abertelrud

Tests/WorkspaceTests/WorkspaceTests.swift

@@ -3806,40 +3806,48 @@ final class WorkspaceTests: XCTestCase {
 
     // This verifies that the simplest possible loading APIs are available for package clients.
     func testSimpleAPI() throws {
-        // This checkout of the SwiftPM package.
-        let packagePath = AbsolutePath(#file).parentDirectory.parentDirectory.parentDirectory
+        try testWithTemporaryDirectory { path in
+            // Create a temporary package as a test case.
+            let packagePath = path.appending(component: "MyPkg")
+            let initPackage = try InitPackage(name: packagePath.basename, destinationPath: packagePath, packageType: .executable)
+            try initPackage.writePackageStructure()
+            
+            // Load the workspace.
+            let observability = ObservabilitySystem.bootstrapForTesting()
+            let workspace = try Workspace(forRootPackage: packagePath, customToolchain: UserToolchain.default)
 
-        let observability = ObservabilitySystem.bootstrapForTesting()
-        let workspace = try Workspace(forRootPackage: packagePath, customToolchain: UserToolchain.default)
-
-        // From here the API should be simple and straightforward:
-        let manifest = try tsc_await {
-            workspace.loadRootManifest(
-                at: packagePath,
-                diagnostics: ObservabilitySystem.topScope.makeDiagnosticsEngine(),
-                completion: $0
-            )
-        }
-        XCTAssertFalse(observability.hasErrorDiagnostics)
+            // From here the API should be simple and straightforward:
+            let manifest = try tsc_await {
+                workspace.loadRootManifest(
+                    at: packagePath,
+                    diagnostics: ObservabilitySystem.topScope.makeDiagnosticsEngine(),
+                    completion: $0
+                )
+            }
+            XCTAssertFalse(observability.hasWarningDiagnostics, observability.diagnostics.description)
+            XCTAssertFalse(observability.hasErrorDiagnostics, observability.diagnostics.description)
 
-        let package = try tsc_await {
-            workspace.loadRootPackage(
-                at: packagePath,
-                diagnostics: ObservabilitySystem.topScope.makeDiagnosticsEngine(),
-                completion: $0
-            )
-        }
-        XCTAssertFalse(observability.hasErrorDiagnostics)
+            let package = try tsc_await {
+                workspace.loadRootPackage(
+                    at: packagePath,
+                    diagnostics: ObservabilitySystem.topScope.makeDiagnosticsEngine(),
+                    completion: $0
+                )
+            }
+            XCTAssertFalse(observability.hasWarningDiagnostics, observability.diagnostics.description)
+            XCTAssertFalse(observability.hasErrorDiagnostics, observability.diagnostics.description)
 
-        let graph = try workspace.loadPackageGraph(
-            rootPath: packagePath,
-            diagnostics: ObservabilitySystem.topScope.makeDiagnosticsEngine()
-        )
-        XCTAssertFalse(observability.hasErrorDiagnostics)
+            let graph = try workspace.loadPackageGraph(
+                rootPath: packagePath,
+                diagnostics: ObservabilitySystem.topScope.makeDiagnosticsEngine()
+            )
+            XCTAssertFalse(observability.hasWarningDiagnostics, observability.diagnostics.description)
+            XCTAssertFalse(observability.hasErrorDiagnostics, observability.diagnostics.description)
 
-        XCTAssertEqual(manifest.name, "SwiftPM")
-        XCTAssertEqual(package.manifestName, manifest.name)
-        XCTAssert(graph.reachableProducts.contains(where: { $0.name == "SwiftPM" }))
+            XCTAssertEqual(manifest.name, "MyPkg")
+            XCTAssertEqual(package.manifestName, manifest.name)
+            XCTAssert(graph.reachableProducts.contains(where: { $0.name == "MyPkg" }))
+        }
     }
 
     func testRevisionDepOnLocal() throws {