Migrate PluginTests to Swift Testing

Sources/SwiftBuildSupport/PIFBuilder.swift

@@ -359,22 +359,20 @@ public final class PIFBuilder {
                             buildCommands: result.buildCommands.map( { buildCommand in
                                 var newEnv: Environment = buildCommand.configuration.environment
 
-                                if let runtimeLibPaths = try? buildParameters.toolchain.runtimeLibraryPaths {
-                                    for libPath in runtimeLibPaths {
-                                        newEnv.appendPath(key: .libraryPath, value: libPath.pathString)
-                                    }
-                                }
+                                let runtimeLibPaths = buildParameters.toolchain.runtimeLibraryPaths
 
-                                let workingDir = buildCommand.configuration.workingDirectory
+                                for libPath in runtimeLibPaths {
+                                    newEnv.appendPath(key: .libraryPath, value: libPath.pathString)
+                                }
 
-                                let writableDirectories: [AbsolutePath] = buildCommand.outputFiles
+                                let writableDirectories: [AbsolutePath] = [pluginOutputDir]
 
                                 return PackagePIFBuilder.CustomBuildCommand(
                                     displayName: buildCommand.configuration.displayName,
                                     executable: buildCommand.configuration.executable.pathString,
                                     arguments: buildCommand.configuration.arguments,
                                     environment: .init(newEnv),
-                                    workingDir: workingDir,
+                                    workingDir: package.path,
                                     inputPaths: buildCommand.inputFiles,
                                     outputPaths: buildCommand.outputFiles.map(\.pathString),
                                     sandboxProfile:

Sources/_InternalTestSupport/Observability.swift

@@ -103,6 +103,18 @@ public func XCTAssertNoDiagnostics(
     XCTFail("Found unexpected diagnostics: \n\(description)", file: file, line: line)
 }
 
+public func expectNoDiagnostics(
+    _ diagnostics: [Basics.Diagnostic],
+    problemsOnly: Bool = true,
+    sourceLocation: SourceLocation = #_sourceLocation
+) {
+    let diagnostics = problemsOnly ? diagnostics.filter { $0.severity >= .warning } : diagnostics
+    if diagnostics.isEmpty { return }
+
+    let description = diagnostics.map { "- " + $0.description }.joined(separator: "\n")
+    Issue.record("Found unexpected diagnostics: \n\(description)", sourceLocation: sourceLocation)
+}
+
 public func testDiagnostics(
     _ diagnostics: [Basics.Diagnostic],
     problemsOnly: Bool = true,