anchor.diff:            .file("out.css", equalsIgnoringWhitespace("a { b: c; }"))
             .validate();
   
  -      sass = await runSass(["--no-source-map", "--update", "-:out.css"]);
  +      sass = await update(["-:out.css"]);
         sass.stdin.writeln("x {y: z}");
         sass.stdin.close();
         expect(sass.stdout, emits('Compiled stdin to out.css.'));
  
positive.code:       await tick;
        await d.file("test2.scss", "d {e: f}").create();
  
        var sass = await runSass([
          "--no-source-map",
          "--update",
          "test1.scss:out1.css",
          "test2.scss:out2.css"
        ]);
        expect(sass.stdout, emits('Compiled test2.scss to out2.css.'));
        await sass.shouldExit(0);
  
  
negative.code: 
    group("doesn't allow", () {
      test("--stdin", () async {
        var sass = await update(["--stdin", "test.scss"]);
        expect(sass.stdout, emits('--update is not allowed with --stdin.'));
        await sass.shouldExit(64);
      });
  
      test("printing to stderr", () async {
        var sass = await update(["test.scss"]);
        expect(sass.stdout,
            emits('--update is not allowed when printing to stdout.'));
        await sass.shouldExit(64);
  