CLI: Add support for watching .json, .cjs, and .mjs files

And add tests for verifying which files are and aren't reacted to,
including coverage for the existing ignoring of events from
"node_modules".

This is prep for #1669.

src/cli/run.js

@@ -184,13 +184,17 @@ run.watch = function watch() {
 	const args = Array.prototype.slice.call( arguments );
 	const baseDir = process.cwd();
 
+	// Include ".json" for test suites that use a data files,
+	// and for changes to package.json that may affect how a file is parsed (e.g. type=module).
+	const includeExts = [ ".js", ".json", ".cjs", ".mjs" ];
+
 	const watcher = watch( baseDir, {
 		persistent: true,
 		recursive: true,
 		delay: 0,
 		filter: ( fullpath ) => {
 			return !/\/node_modules\//.test( fullpath ) &&
-				/\.js$/.test( fullpath );
+				includeExts.includes( path.extname( fullpath ) );
 		}
 	}, ( event, fullpath ) => {
 		console.log( `File ${event}: ${path.relative( baseDir, fullpath )}` );

test/cli/cli-watch.js

@@ -28,6 +28,10 @@ if ( process.platform === "win32" ) {
 }
 
 QUnit.module( "CLI Watch", function( hooks ) {
+	hooks.before( function() {
+		rimraf.sync( fixturePath );
+	} );
+
 	hooks.beforeEach( function() {
 		fs.mkdirSync( path.dirname( fixturePath ), { recursive: true } );
 		fixturify.writeSync( fixturePath, {
@@ -171,6 +175,56 @@ QUnit.module( "CLI Watch", function( hooks ) {
 		assert.equal( result.stdout, expectedWatchOutput[ "remove-file" ] );
 	} );
 
+	// Skip in coverage mode since NYC adds non-default extensions
+	QUnit[ process.env.NYC_PROCESS_ID ? "skip" : "test" ]( "default file extensions", async assert => {
+		fixturify.writeSync( fixturePath, {
+			"tests": {
+				"setup.js": "QUnit.on('runEnd', function() { process.send('runEnd'); });",
+				"foo.js": "QUnit.test('foo', function(assert) { assert.true(true); });"
+			}
+		} );
+
+		const command = [ "qunit", "--watch", "watching/tests" ];
+		const result = await executeIpc(
+			command,
+			execution => {
+				execution.once( "message", () => {
+					fixturify.writeSync( fixturePath, {
+						"x.cjs": "-",
+						"x.js": "-",
+						"x.json": "-",
+						"x.mjs": "-",
+						"x.ts": "-",
+						"x.txt": "-",
+
+						"node_modules": {
+							"x": {
+								"y.js": "-"
+							}
+						},
+
+						"tests": {
+							"foo.js": "QUnit.test('foo2', function(assert) { assert.true(true); });",
+							"setup.js": "QUnit.on('runEnd', function() { process.send('runEnd2'); });"
+						}
+					} );
+
+					execution.once( "message", data => {
+
+						// Ignore other re-runs
+						if ( data === "runEnd2" ) {
+							kill( execution );
+						}
+					} );
+				} );
+			}
+		);
+
+		assert.equal( result.code, 0 );
+		assert.equal( result.stderr, "" );
+		assert.equal( result.stdout, expectedWatchOutput[ "file-extensions" ] );
+	} );
+
 	QUnit.test( "aborts and restarts when in middle of run", async assert => {
 
 		// A proper abort finishes the currently running test and runs any remaining

test/cli/fixtures/expected/watch-tap-outputs.js

@@ -62,6 +62,29 @@ ok 1 foo
 # skip 0
 # todo 0
 # fail 0
+Stopping QUnit...`,
+
+	"file-extensions": `TAP version 13
+ok 1 foo
+1..1
+# pass 1
+# skip 0
+# todo 0
+# fail 0
+File update: watching/x.cjs
+File update: watching/x.js
+File update: watching/x.json
+File update: watching/x.mjs
+File update: watching/tests/foo.js
+File update: watching/tests/setup.js
+Restarting...
+TAP version 13
+ok 1 foo2
+1..1
+# pass 1
+# skip 0
+# todo 0
+# fail 0
 Stopping QUnit...`,
 
 	"change-file-mid-run": `TAP version 13

test/cli/helpers/execute.js

@@ -110,7 +110,7 @@ module.exports.execute = async function execute( command, options = {}, hook ) {
 			result.code = exitCode;
 			const stderr = normalize( String( result.stderr ).trimEnd() );
 			if ( exitCode !== 0 ) {
-				reject( new Error( "Error code " + exitCode + "\n" + stderr ) );
+				reject( new Error( "Error code " + exitCode + "\n" + ( stderr || result.stdout ) ) );
 			} else {
 				resolve();
 			}