Ensure root level hooks are called when running in watch mode

## Rationale
Tests with root level hooks are ignored when running in watch mode.
This occurs on initial & subsequent runs.

## Changes

- extended `suite.clone` to clone hooks

This change was necessary to ensure that when a suite is cloned during
the setup phase for watch that hooks are available on the newly cloned
suite.

Note the use of `suite.clone` appears to be only used in
`lib/cli/run-watch`. I did consider making the cloning of hooks
optional but opted not to as `suite.clone` is internal to `mocha` & not
publicly referenced in the API documentation.

Tests for `suite.clone` have been amended to reflect the above change.

- Extended integration tests for watch to take into consideration
  hooks

## Refs

- mochajs/issues/4347

lib/suite.js

@@ -119,6 +119,13 @@ Suite.prototype.clone = function() {
   debug('clone');
   suite.ctx = this.ctx;
   suite.root = this.root;
+
+  // Required to ensure hooks are available during watch
+  suite._beforeEach = this._beforeEach;
+  suite._afterEach = this._afterEach;
+  suite._beforeAll = this._beforeAll;
+  suite._afterAll = this._afterAll;
+
   suite.timeout(this.timeout());
   suite.retries(this.retries());
   suite.slow(this.slow());

test/integration/fixtures/options/watch/hook.fixture.js

@@ -0,0 +1,7 @@
+module.exports = {
+  mochaHooks: {
+    ["<hook>"]: function() {
+      throw new Error("<hook> Hook Error");
+    },
+  },
+};

test/integration/options/watch.spec.js

@@ -275,6 +275,43 @@ describe('--watch', function() {
         expect(results[1].tests, 'to have length', 2);
       });
     });
+
+    describe('with required hooks', function() {
+      /**
+       * Helper for setting up hook tests
+       *
+       * @param {string} hookName name of hook to test
+       * @return {function}
+       */
+      function setupHookTest(hookName) {
+        return function() {
+          const testFile = path.join(tempDir, 'test.js');
+          const hookFile = path.join(tempDir, 'hook.js');
+
+          copyFixture('__default__', testFile);
+          copyFixture('options/watch/hook', hookFile);
+
+          replaceFileContents(hookFile, '<hook>', hookName);
+
+          return runMochaWatch(
+            [testFile, '--require', hookFile],
+            tempDir,
+            () => {
+              touchFile(testFile);
+            }
+          ).then(results => {
+            expect(results.length, 'to equal', 2);
+            expect(results[0].failures, 'to have length', 1);
+            expect(results[1].failures, 'to have length', 1);
+          });
+        };
+      }
+
+      it('mochaHooks.beforeAll runs as expected', setupHookTest('beforeAll'));
+      it('mochaHooks.beforeEach runs as expected', setupHookTest('beforeEach'));
+      it('mochaHooks.afterAll runs as expected', setupHookTest('afterAll'));
+      it('mochaHooks.afterEach runs as expected', setupHookTest('afterEach'));
+    });
   });
 });
 

test/unit/suite.spec.js

@@ -54,20 +54,20 @@ describe('Suite', function() {
       expect(this.suite.clone().tests, 'to be empty');
     });
 
-    it('should not copy the values from the _beforeEach array', function() {
-      expect(this.suite.clone()._beforeEach, 'to be empty');
+    it('should copy the values from the _beforeEach array', function() {
+      expect(this.suite.clone()._beforeEach, 'to equal', [2]);
     });
 
-    it('should not copy the values from the _beforeAll array', function() {
-      expect(this.suite.clone()._beforeAll, 'to be empty');
+    it('should copy the values from the _beforeAll array', function() {
+      expect(this.suite.clone()._beforeAll, 'to equal', [3]);
     });
 
-    it('should not copy the values from the _afterEach array', function() {
-      expect(this.suite.clone()._afterEach, 'to be empty');
+    it('should copy the values from the _afterEach array', function() {
+      expect(this.suite.clone()._afterEach, 'to equal', [4]);
     });
 
-    it('should not copy the values from the _afterAll array', function() {
-      expect(this.suite.clone()._afterAll, 'to be empty');
+    it('should copy the values from the _afterAll array', function() {
+      expect(this.suite.clone()._afterAll, 'to equal', [5]);
     });
 
     it('should copy the root property', function() {