Address review

Author: David Ungar

Tests/SwiftDriverTests/IncrementalCompilationTests.swift

@@ -340,9 +340,13 @@ final class IncrementalCompilationTests: XCTestCase {
     try? localFileSystem.removeFileTree(tempDir)
   }
 
-  func prepare(line: Int = #line) {
-    // ensure tempDir is unique by using line prefix
-    self.tempDir = try! withTemporaryDirectory(prefix: line.description, removeTreeOnDeinit: false) {$0}
+  override func setUp() {
+    // Prefix directory with test name to ensure directory name is unique when
+    // testing in parallel.
+    // name returns e.g. "[SwiftDriverTests.IncrementalCompilationTests testIncremental]
+    // but we just want "testIncremental"
+    let testName = name.split(separator: " ").last!.dropLast()
+    self.tempDir = try! withTemporaryDirectory(prefix: String(testName),  removeTreeOnDeinit: false) {$0}
     try! localFileSystem.createDirectory(derivedDataPath)
     writeOutputFileMapData(module: module,
                            inputPaths: inputPathsAndContents.map {$0.0},
@@ -356,14 +360,11 @@ final class IncrementalCompilationTests: XCTestCase {
     }
   }
 
-  // FIXME: why does it fail on Linux in CI?
   func testIncrementalDiagnostics() throws {
-    prepare()
     try testIncremental(checkDiagnostics: true)
   }
 
   func testIncremental() throws {
-    prepare()
     try testIncremental(checkDiagnostics: false)
   }
 
@@ -554,7 +555,6 @@ final class IncrementalCompilationTests: XCTestCase {
   /// autolink job.
   /// Much of the code below is taking from testLinking(), but uses the output file map code here.
   func testAutolinkOutputPath() {
-    prepare()
     var env = ProcessEnv.vars
     env["SWIFT_DRIVER_TESTS_ENABLE_EXEC_PATH_FALLBACK"] = "1"
     env["SWIFT_DRIVER_SWIFT_AUTOLINK_EXTRACT_EXEC"] = "/garbage/swift-autolink-extract"