Added a test for formating

src/format.ts

@@ -18,7 +18,6 @@ import * as jsdiff from 'diff';
 import * as entities from 'entities';
 import * as fs from 'fs';
 import * as path from 'path';
-import {file, fileSync} from 'tmp';
 
 import {Options} from './cli';
 import {createProgram} from './lint';
@@ -156,6 +155,7 @@ function getReplacements(fileXML: string): Replacement[] {
   const replacements: Replacement[] = [];
 
   let xmlLines = fileXML.split('\n');
+  // The first and last two elements in xmlLines are not needed
   xmlLines = xmlLines.slice(1, xmlLines.length - 2);
 
   for (let i = 0; i < xmlLines.length; i++) {
@@ -239,7 +239,7 @@ function printDiffs(diffs: jsdiff.IUniDiff, options: Options) {
       } else if (line[0] === '+') {
         options.logger.log('   ' + chalk.green(line));
       } else {
-        options.logger.log('   ' + chalk.black(line));
+        options.logger.log('   ' + chalk.gray(line));
       }
     });
     options.logger.log('\n');

test/test-format.ts

@@ -25,8 +25,11 @@ import {nop} from '../src/util';
 import {withFixtures} from './fixtures';
 
 // clang-format won't pass this code because of trailing spaces.
-const BAD_CODE = 'export const foo = [ 2 ];';
-const GOOD_CODE = 'export const foo = [2];';
+const BAD_CODE = '//🦄\nexport const foo = [ \"2\" ];';
+const GOOD_CODE = '//🦄\nexport const foo = [\'2\'];';
+
+const CLANG_FORMAT_MESSAGE =
+    'clang-format reported errors... run `gts fix` to address.';
 
 const OPTIONS: Options = {
   gtsRootDir: path.resolve(__dirname, '../..'),
@@ -210,3 +213,32 @@ test.serial('format should return error from failed spawn', async t => {
         format.clangFormat.spawnClangFormat = original;
       });
 });
+
+test.serial(
+    'format should print suggestions for fixes for ill-formatted file', t => {
+      return withFixtures(
+          {
+            'tsconfig.json': JSON.stringify({files: ['a.ts']}),
+            'a.ts': BAD_CODE
+          },
+          async () => {
+            let output = '';
+            const newLogger = Object.assign({}, OPTIONS.logger, {
+              log: (n: string) => {
+                output += n;
+              }
+            });
+            const options = Object.assign({}, OPTIONS, {logger: newLogger});
+
+            await format.format(options, [], false);
+            if (output.search(CLANG_FORMAT_MESSAGE) === -1) {
+              t.fail('Does not print ...run \'gts fix\'...');
+            } else if (
+                output.indexOf('+export const foo = [\'2\'];') === -1 ||
+                output.indexOf('-export const foo = [ \"2\" ];') === -1 ||
+                output.indexOf('🦄') === -1) {
+              t.fail('Output messages and suggested fix are incorrect');
+            }
+            t.pass();
+          });
+    });