watch mode always runs all exclusive tests

Fixes #635.

docs/recipes/watch-mode.md

@@ -69,6 +69,10 @@ AVA tracks which source files your test files depend on. If you change such a de
 
 Dependency tracking works for required modules. Custom extensions and transpilers are supported, provided you loaded them using the [`--require` CLI flag] and not from inside your test file. Files accessed using the `fs` module are not tracked.
 
+## Watch mode and the `.only` modifier
+
+The `.only` modifier disables watch mode's dependency tracking algorithm. When a change is made, all `.only` tests will be rerun, regardless of whether the test depends on the changed file.
+
 ## Manually rerunning all tests
 
 You can quickly rerun all tests by typing <kbd>r</kbd> on the console, followed by <kbd>Enter</kbd>.
@@ -96,3 +100,4 @@ Watch mode is relatively new and there might be some rough edges. Please [report
 [`ignore-by-default`]: https://github.com/novemberborn/ignore-by-default
 [`--require` CLI flag]: https://github.com/sindresorhus/ava#cli
 [`--source` CLI flag]: https://github.com/sindresorhus/ava#cli
+[`.only` modifier]: https://github.com/sindresorhus/ava#running-specific-tests

lib/watcher.js

@@ -47,6 +47,13 @@ function Watcher(logger, api, files, sources) {
 			}, this);
 
 			runOnlyExclusive = exclusiveFiles.length !== this.filesWithExclusiveTests.length;
+
+			if (runOnlyExclusive) {
+				// The test files that previously contained exclusive tests are always
+				// run, together with the remaining specific files.
+				var remainingFiles = diff(specificFiles, exclusiveFiles);
+				specificFiles = this.filesWithExclusiveTests.concat(remainingFiles);
+			}
 		}
 
 		this.busy = api.run(specificFiles || files, {

test/watcher.js

@@ -938,7 +938,7 @@ group('chokidar is installed', function (beforeEach, test, group) {
 			change(t4);
 			return debounce(2).then(function () {
 				t.ok(api.run.calledTwice);
-				t.same(api.run.secondCall.args, [[t3, t4], {runOnlyExclusive: true}]);
+				t.same(api.run.secondCall.args, [[t1, t2, t3, t4], {runOnlyExclusive: true}]);
 			});
 		});
 
@@ -950,7 +950,7 @@ group('chokidar is installed', function (beforeEach, test, group) {
 			change(t4);
 			return debounce(2).then(function () {
 				t.ok(api.run.calledTwice);
-				t.same(api.run.secondCall.args, [[t1, t4], {runOnlyExclusive: true}]);
+				t.same(api.run.secondCall.args, [[t1, t2, t4], {runOnlyExclusive: true}]);
 			});
 		});