             }
 
             let thisDirectoryContents = try vfs.getDirectoryContents(AbsolutePath("/"))
-            XCTAssertTrue(!thisDirectoryContents.contains(where: { $0 == "." }))
-            XCTAssertTrue(!thisDirectoryContents.contains(where: { $0 == ".." }))
+            XCTAssertFalse(thisDirectoryContents.contains(where: { $0 == "." }))
+            XCTAssertFalse(thisDirectoryContents.contains(where: { $0 == ".." }))
             XCTAssertEqual(thisDirectoryContents.sorted(), ["best", "dir", "exec-foo", "exec-sym", "hello"])
 
             let contents = try vfs.getDirectoryContents(AbsolutePath("/dir"))

            let vfs = try VirtualFileSystem(path: vfsPath.path, fs: fs)

            // exists()
            XCTAssert(vfs.exists(AbsolutePath("/")))
            XCTAssert(!vfs.exists(AbsolutePath("/does-not-exist")))

            // isFile()
            let filePath = AbsolutePath("/best")

            XCTAssertEqual(execFileContents, ByteString(contents))

            // isDirectory()
            XCTAssertTrue(vfs.isDirectory(AbsolutePath("/")))
            XCTAssertFalse(vfs.isDirectory(AbsolutePath("/does-not-exist")))

            // getDirectoryContents()
            do {
