             let vfs = try VirtualFileSystem(path: vfsPath.path, fs: fs)
 
             // exists()
-            XCTAssert(vfs.exists(AbsolutePath("/")))
-            XCTAssert(!vfs.exists(AbsolutePath("/does-not-exist")))
+            XCTAssertTrue(vfs.exists(AbsolutePath("/")))
+            XCTAssertFalse(vfs.exists(AbsolutePath("/does-not-exist")))
 
             // isFile()
             let filePath = AbsolutePath("/best")

            }

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

            let contents = try vfs.getDirectoryContents(AbsolutePath("/dir"))

            XCTAssertEqual(execFileContents, ByteString(contents))

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

            // getDirectoryContents()
            do {
