 
   func touch(_ name: String) {
     print("*** touching \(name) ***", to: &stderrStream); stderrStream.flush()
-    let (path, contents) = inputPathsAndContents.filter {$0.0.pathString.contains(name)}.first!
+    let (path, contents) = try! XCTUnwrap(inputPathsAndContents.filter {$0.0.pathString.contains(name)}.first)
     try! localFileSystem.writeFileContents(path) { $0 <<< contents }
   }
 
   private func replace(contentsOf name: String, with replacement: String ) {
     print("*** replacing \(name) ***", to: &stderrStream); stderrStream.flush()
-    let path = inputPathsAndContents.filter {$0.0.pathString.contains("/" + name + ".swift")}.first!.0
+    let path = try! XCTUnwrap(inputPathsAndContents.filter {$0.0.pathString.contains("/" + name + ".swift")}.first).0
     let previousContents = try! localFileSystem.readFileContents(path).cString
     try! localFileSystem.writeFileContents(path) { $0 <<< replacement }
     let newContents = try! localFileSystem.readFileContents(path).cString

        + ["-emit-library", "-target", "x86_64-unknown-linux"],
      env: env)
    let plannedJobs = try! driver.planBuild()
    let autolinkExtractJob = plannedJobs
      .filter { $0.kind == .autolinkExtract }
      .first!
    let autoOuts = autolinkExtractJob.outputs.filter {$0.type == .autolink}
    XCTAssertEqual(autoOuts.count, 1)
    let autoOut = autoOuts[0]


    XCTAssertEqual(try! buildRecord.inputInfos[VirtualPath(path: file2 )]!.status,
                   .needsCascadingBuild)
    XCTAssert(try! isCloseEnough(
                XCTUnwrap(buildRecord.inputInfos[VirtualPath(path: file2 )])
                  .previousModTime.legacyDriverSecsAndNanos,
                [1570318778, 0]))
    XCTAssertEqual(try! XCTUnwrap(buildRecord.inputInfos[VirtualPath(path: gazorp)]).status,
                   .needsNonCascadingBuild)
    XCTAssertEqual(try! XCTUnwrap(buildRecord.inputInfos[VirtualPath(path: gazorp)])
                    .previousModTime.legacyDriverSecsAndNanos,
                   [0, 0])
    XCTAssertEqual(try! XCTUnwrap(buildRecord.inputInfos[VirtualPath(path: main  )]).status,
                   .upToDate)
    XCTAssert(try! isCloseEnough( XCTUnwrap(buildRecord.inputInfos[VirtualPath(path: main  )])
                                    .previousModTime.legacyDriverSecsAndNanos,
                                  [1570083660, 0]))

