Deprecation message when an async Suites are used

lib/interfaces/common.js

@@ -145,7 +145,16 @@ module.exports = function (suites, context, mocha) {
           throw createUnsupportedError('Pending test forbidden');
         }
         if (typeof opts.fn === 'function') {
-          opts.fn.call(suite);
+          const suiteResult = opts.fn.call(suite);
+          if (suiteResult instanceof Promise) {
+            errors.deprecate(
+              'Suite "' +
+                suite.fullTitle() +
+                '" returned a Promise. ' +
+                'Asynchronous suites are not supported, use a ' +
+                'synchronous callback instead.'
+            );
+          }
           suites.shift();
         } else if (typeof opts.fn === 'undefined' && !suite.pending) {
           throw createMissingArgumentError(

test/integration/fixtures/suite/suite-async-callback.fixture.js

@@ -0,0 +1,3 @@
+'use strict';
+
+describe('a suite without an async callback', async function () {});

test/integration/suite.spec.js

@@ -72,3 +72,24 @@ describe('suite returning a value', function () {
     );
   });
 });
+
+describe('suite w/async callback', function () {
+  it('should print a helpful deprecation message when a callback for suite is async', function (done) {
+    run(
+      'suite/suite-async-callback.fixture.js',
+      args,
+      function (err, res) {
+        if (err) {
+          return done(err);
+        }
+        expect(
+          res.output,
+          'to match',
+          /Asynchronous suites are not supported, use a synchronous callback instead./
+        );
+        done();
+      },
+      {stdio: 'pipe'}
+    );
+  });
+});