Add --grep flag to gulp test

.github/CONTRIBUTING.md

@@ -45,9 +45,10 @@ When submitting a PR, please fill out the template that is presented by GitHub w
     # Or run tests by selecting the appropriate drop down option
 
     # Alternatively, build and run tests through gulp and npm scripts
-    gulp build            # build
-    npm test              # test
-    gulp test             # run tests inside Docker container
+    gulp build                  # build
+    npm test                    # test
+    gulp test                   # run tests inside Docker container
+    gulp test --grep testSuite  # run only tests/suites filtered by js regex inside container
     ```
 
 ## Code Architecture

gulpfile.js

@@ -178,6 +178,13 @@ gulp.task('forceprettier', function(done) {
 
 // test
 gulp.task('test', function(done) {
+  // the flag --grep takes js regex as a string and filters by test and test suite names
+  var knownOptions = {
+    string: 'grep',
+    default: { grep: '' },
+  };
+  var options = minimist(process.argv.slice(2), knownOptions);
+
   var spawn = require('child_process').spawn;
   const dockerTag = 'vscodevim';
 
@@ -200,8 +207,17 @@ gulp.task('test', function(done) {
       );
     }
 
+    const dockerRunArgs = [
+      'run',
+      '-it',
+      '--env',
+      `MOCHA_GREP=${options.grep}`,
+      '-v',
+      process.cwd() + ':/app',
+      dockerTag,
+    ];
     console.log('Running tests inside container...');
-    var dockerRunCmd = spawn('docker', ['run', '-it', '-v', process.cwd() + ':/app', dockerTag], {
+    var dockerRunCmd = spawn('docker', dockerRunArgs, {
       cwd: process.cwd(),
       stdio: 'inherit',
     });

test/index.ts

@@ -17,10 +17,15 @@ Globals.mockConfiguration = new Configuration();
 
 // See https://github.com/mochajs/mocha/wiki/Using-mocha-programmatically#set-options for more info
 var testRunner = require('vscode/lib/testrunner');
-testRunner.configure({
+// create new RegExp to catch errors early, ie before passing it to mocha
+const mochaGrep = new RegExp(process.env.MOCHA_GREP || '');
+const testRunnerConfiguration: MochaSetupOptions = {
   ui: 'tdd',
   useColors: true,
   timeout: 10000,
-});
+  grep: mochaGrep,
+};
+
+testRunner.configure(testRunnerConfiguration);
 
 module.exports = testRunner;