anchor.diff:        await d.file("test.scss", "a {b: c}").create();
         await d.file("out.css", "x {y: z}").create();
   
  -      var sass =
  -          await runSass(["--no-source-map", "--update", "test.scss:out.css"]);
  +      var sass = await update(["test.scss:out.css"]);
         expect(sass.stdout, emitsDone);
         await sass.shouldExit(0);
   
  
positive.code:       await d.file("other.scss", "a {b: c}").create();
        await d.file("test.scss", "@import 'other'").create();
  
        var sass =
            await runSass(["--no-source-map", "--update", "test.scss:out.css"]);
        expect(sass.stdout, emits('Compiled test.scss to out.css.'));
        await sass.shouldExit(0);
  
        await tick;
        await d.file("other.scss", "x {y: z}").create();
  
        sass =
            await runSass(["--no-source-map", "--update", "test.scss:out.css"]);
        expect(sass.stdout, emits('Compiled test.scss to out.css.'));
        await sass.shouldExit(0);
  
  
negative.code:           .file("out.css", equalsIgnoringWhitespace("a { b: c; }"))
            .validate();
  
        sass = await update(["-:out.css"]);
        sass.stdin.writeln("x {y: z}");
        sass.stdin.close();
        expect(sass.stdout, emits('Compiled stdin to out.css.'));
  