diff --git a/flask/testsuite/__init__.py b/flask/testsuite/__init__.py
index 9088fc52..72de1963 100644
--- a/flask/testsuite/__init__.py
+++ b/flask/testsuite/__init__.py
@@ -103,7 +103,7 @@ def emits_module_deprecation_warning(f):
             f(self, *args, **kwargs)
             self.assert_true(log, 'expected deprecation warning')
             for entry in log:
-                self.assert_true('Modules are deprecated' in str(entry['message']))
+                self.assert_in('Modules are deprecated', str(entry['message']))
     return update_wrapper(new_f, f)
 
 
@@ -145,6 +145,12 @@ class FlaskTestCase(unittest.TestCase):
     def assert_true(self, x, msg=None):
         self.assertTrue(x, msg)
 
+    def assert_in(self, x, y):
+        self.assertIn(x, y)
+
+    def assert_not_in(self, x, y):
+        self.assertNotIn(x, y)
+
 
 class _ExceptionCatcher(object):
 
diff --git a/flask/testsuite/basic.py b/flask/testsuite/basic.py
index 20c2f0cc..0abcac10 100644
--- a/flask/testsuite/basic.py
+++ b/flask/testsuite/basic.py
@@ -173,8 +173,8 @@ class BasicFunctionalityTestCase(FlaskTestCase):
             flask.session['testing'] = 42
             return 'Hello World'
         rv = app.test_client().get('/', 'http://example.com/')
-        self.assert_true('domain=.example.com' in rv.headers['set-cookie'].lower())
-        self.assert_true('httponly' in rv.headers['set-cookie'].lower())
+        self.assert_in('domain=.example.com', rv.headers['set-cookie'].lower())
+        self.assert_in('httponly', rv.headers['set-cookie'].lower())
 
     def test_session_using_server_name_and_port(self):
         app = flask.Flask(__name__)
@@ -187,8 +187,8 @@ class BasicFunctionalityTestCase(FlaskTestCase):
             flask.session['testing'] = 42
             return 'Hello World'
         rv = app.test_client().get('/', 'http://example.com:8080/')
-        self.assert_true('domain=.example.com' in rv.headers['set-cookie'].lower())
-        self.assert_true('httponly' in rv.headers['set-cookie'].lower())
+        self.assert_in('domain=.example.com', rv.headers['set-cookie'].lower())
+        self.assert_in('httponly', rv.headers['set-cookie'].lower())
 
     def test_session_using_server_name_port_and_path(self):
         app = flask.Flask(__name__)
@@ -202,9 +202,9 @@ class BasicFunctionalityTestCase(FlaskTestCase):
             flask.session['testing'] = 42
             return 'Hello World'
         rv = app.test_client().get('/', 'http://example.com:8080/foo')
-        self.assert_true('domain=example.com' in rv.headers['set-cookie'].lower())
-        self.assert_true('path=/foo' in rv.headers['set-cookie'].lower())
-        self.assert_true('httponly' in rv.headers['set-cookie'].lower())
+        self.assert_in('domain=example.com', rv.headers['set-cookie'].lower())
+        self.assert_in('path=/foo', rv.headers['set-cookie'].lower())
+        self.assert_in('httponly', rv.headers['set-cookie'].lower())
 
     def test_session_using_application_root(self):
         class PrefixPathMiddleware(object):
@@ -226,7 +226,7 @@ class BasicFunctionalityTestCase(FlaskTestCase):
             flask.session['testing'] = 42
             return 'Hello World'
         rv = app.test_client().get('/', 'http://example.com:8080/')
-        self.assert_true('path=/bar' in rv.headers['set-cookie'].lower())
+        self.assert_in('path=/bar', rv.headers['set-cookie'].lower())
 
     def test_session_using_session_settings(self):
         app = flask.Flask(__name__)
@@ -245,10 +245,10 @@ class BasicFunctionalityTestCase(FlaskTestCase):
             return 'Hello World'
         rv = app.test_client().get('/', 'http://www.example.com:8080/test/')
         cookie = rv.headers['set-cookie'].lower()
-        self.assert_true('domain=.example.com' in cookie)
-        self.assert_true('path=/;' in cookie)
-        self.assert_true('secure' in cookie)
-        self.assert_true('httponly' not in cookie)
+        self.assert_in('domain=.example.com', cookie)
+        self.assert_in('path=/;', cookie)
+        self.assert_in('secure', cookie)
+        self.assert_not_in('httponly', cookie)
 
     def test_missing_session(self):
         app = flask.Flask(__name__)
@@ -280,7 +280,7 @@ class BasicFunctionalityTestCase(FlaskTestCase):
 
         client = app.test_client()
         rv = client.get('/')
-        self.assert_true('set-cookie' in rv.headers)
+        self.assert_in('set-cookie', rv.headers)
         match = re.search(r'\bexpires=([^;]+)', rv.headers['set-cookie'])
         expires = parse_date(match.group())
         expected = datetime.utcnow() + app.permanent_session_lifetime
@@ -293,7 +293,7 @@ class BasicFunctionalityTestCase(FlaskTestCase):
 
         permanent = False
         rv = app.test_client().get('/')
-        self.assert_true('set-cookie' in rv.headers)
+        self.assert_in('set-cookie', rv.headers)
         match = re.search(r'\bexpires=([^;]+)', rv.headers['set-cookie'])
         self.assert_true(match is None)
 
@@ -448,12 +448,12 @@ class BasicFunctionalityTestCase(FlaskTestCase):
             return response
         @app.route('/')
         def index():
-            self.assert_true('before' in evts)
-            self.assert_true('after' not in evts)
+            self.assert_in('before', evts)
+            self.assert_not_in('after', evts)
             return 'request'
-        self.assert_true('after' not in evts)
+        self.assert_not_in('after', evts)
         rv = app.test_client().get('/').data
-        self.assert_true(b'after' in evts)
+        self.assert_in(b'after', evts)
         self.assert_equal(rv, b'request|after')
 
     def test_after_request_processing(self):
@@ -483,7 +483,7 @@ class BasicFunctionalityTestCase(FlaskTestCase):
             return "Response"
         rv = app.test_client().get('/')
         self.assert_equal(rv.status_code, 200)
-        self.assert_true(b'Response' in rv.data)
+        self.assert_in(b'Response', rv.data)
         self.assert_equal(len(called), 1)
 
     def test_teardown_request_handler_debug_mode(self):
@@ -499,7 +499,7 @@ class BasicFunctionalityTestCase(FlaskTestCase):
             return "Response"
         rv = app.test_client().get('/')
         self.assert_equal(rv.status_code, 200)
-        self.assert_true(b'Response' in rv.data)
+        self.assert_in(b'Response', rv.data)
         self.assert_equal(len(called), 1)
 
     def test_teardown_request_handler_error(self):
@@ -532,7 +532,7 @@ class BasicFunctionalityTestCase(FlaskTestCase):
             1/0
         rv = app.test_client().get('/')
         self.assert_equal(rv.status_code, 500)
-        self.assert_true(b'Internal Server Error' in rv.data)
+        self.assert_in(b'Internal Server Error', rv.data)
         self.assert_equal(len(called), 2)
 
     def test_before_after_request_order(self):
@@ -664,8 +664,8 @@ class BasicFunctionalityTestCase(FlaskTestCase):
             try:
                 c.post('/fail', data={'foo': 'index.txt'})
             except DebugFilesKeyError as e:
-                self.assert_true('no file contents were transmitted' in str(e))
-                self.assert_true('This was submitted: "index.txt"' in str(e))
+                self.assert_in('no file contents were transmitted', str(e))
+                self.assert_in('This was submitted: "index.txt"', str(e))
             else:
                 self.fail('Expected exception')
 
@@ -974,7 +974,7 @@ class BasicFunctionalityTestCase(FlaskTestCase):
             def broken():
                 return 'Meh'
         except AssertionError as e:
-            self.assert_true('A setup function was called' in str(e))
+            self.assert_in('A setup function was called', str(e))
         else:
             self.fail('Expected exception')
 
@@ -1008,9 +1008,9 @@ class BasicFunctionalityTestCase(FlaskTestCase):
             try:
                 c.post('/foo', data={})
             except AssertionError as e:
-                self.assert_true('http://localhost/foo/' in str(e))
-                self.assert_true('Make sure to directly send your POST-request '
-                             'to this URL' in str(e))
+                self.assert_in('http://localhost/foo/', str(e))
+                self.assert_in('Make sure to directly send your POST-request '
+                               'to this URL', str(e))
             else:
                 self.fail('Expected exception')
 
diff --git a/flask/testsuite/blueprints.py b/flask/testsuite/blueprints.py
index 088c72d2..89a8f2d7 100644
--- a/flask/testsuite/blueprints.py
+++ b/flask/testsuite/blueprints.py
@@ -547,7 +547,7 @@ class BlueprintTestCase(FlaskTestCase):
             return s[::-1]
         app = flask.Flask(__name__)
         app.register_blueprint(bp, url_prefix='/py')
-        self.assert_true('my_reverse' in app.jinja_env.filters.keys())
+        self.assert_in('my_reverse', app.jinja_env.filters.keys())
         self.assert_equal(app.jinja_env.filters['my_reverse'], my_reverse)
         self.assert_equal(app.jinja_env.filters['my_reverse']('abcd'), 'dcba')
 
@@ -558,7 +558,7 @@ class BlueprintTestCase(FlaskTestCase):
         bp.add_app_template_filter(my_reverse)
         app = flask.Flask(__name__)
         app.register_blueprint(bp, url_prefix='/py')
-        self.assert_true('my_reverse' in app.jinja_env.filters.keys())
+        self.assert_in('my_reverse', app.jinja_env.filters.keys())
         self.assert_equal(app.jinja_env.filters['my_reverse'], my_reverse)
         self.assert_equal(app.jinja_env.filters['my_reverse']('abcd'), 'dcba')
 
@@ -569,7 +569,7 @@ class BlueprintTestCase(FlaskTestCase):
             return s[::-1]
         app = flask.Flask(__name__)
         app.register_blueprint(bp, url_prefix='/py')
-        self.assert_true('strrev' in app.jinja_env.filters.keys())
+        self.assert_in('strrev', app.jinja_env.filters.keys())
         self.assert_equal(app.jinja_env.filters['strrev'], my_reverse)
         self.assert_equal(app.jinja_env.filters['strrev']('abcd'), 'dcba')
 
@@ -580,7 +580,7 @@ class BlueprintTestCase(FlaskTestCase):
         bp.add_app_template_filter(my_reverse, 'strrev')
         app = flask.Flask(__name__)
         app.register_blueprint(bp, url_prefix='/py')
-        self.assert_true('strrev' in app.jinja_env.filters.keys())
+        self.assert_in('strrev', app.jinja_env.filters.keys())
         self.assert_equal(app.jinja_env.filters['strrev'], my_reverse)
         self.assert_equal(app.jinja_env.filters['strrev']('abcd'), 'dcba')
 
@@ -656,7 +656,7 @@ class BlueprintTestCase(FlaskTestCase):
             return isinstance(value, bool)
         app = flask.Flask(__name__)
         app.register_blueprint(bp, url_prefix='/py')
-        self.assert_true('is_boolean' in app.jinja_env.tests.keys())
+        self.assert_in('is_boolean', app.jinja_env.tests.keys())
         self.assert_equal(app.jinja_env.tests['is_boolean'], is_boolean)
         self.assert_true(app.jinja_env.tests['is_boolean'](False))
 
@@ -667,7 +667,7 @@ class BlueprintTestCase(FlaskTestCase):
         bp.add_app_template_test(is_boolean)
         app = flask.Flask(__name__)
         app.register_blueprint(bp, url_prefix='/py')
-        self.assert_true('is_boolean' in app.jinja_env.tests.keys())
+        self.assert_in('is_boolean', app.jinja_env.tests.keys())
         self.assert_equal(app.jinja_env.tests['is_boolean'], is_boolean)
         self.assert_true(app.jinja_env.tests['is_boolean'](False))
 
@@ -678,7 +678,7 @@ class BlueprintTestCase(FlaskTestCase):
             return isinstance(value, bool)
         app = flask.Flask(__name__)
         app.register_blueprint(bp, url_prefix='/py')
-        self.assert_true('boolean' in app.jinja_env.tests.keys())
+        self.assert_in('boolean', app.jinja_env.tests.keys())
         self.assert_equal(app.jinja_env.tests['boolean'], is_boolean)
         self.assert_true(app.jinja_env.tests['boolean'](False))
 
@@ -689,7 +689,7 @@ class BlueprintTestCase(FlaskTestCase):
         bp.add_app_template_test(is_boolean, 'boolean')
         app = flask.Flask(__name__)
         app.register_blueprint(bp, url_prefix='/py')
-        self.assert_true('boolean' in app.jinja_env.tests.keys())
+        self.assert_in('boolean', app.jinja_env.tests.keys())
         self.assert_equal(app.jinja_env.tests['boolean'], is_boolean)
         self.assert_true(app.jinja_env.tests['boolean'](False))
 
@@ -704,7 +704,7 @@ class BlueprintTestCase(FlaskTestCase):
         def index():
             return flask.render_template('template_test.html', value=False)
         rv = app.test_client().get('/')
-        self.assert_true(b'Success!' in rv.data)
+        self.assert_in(b'Success!', rv.data)
 
     def test_template_test_after_route_with_template(self):
         app = flask.Flask(__name__)
@@ -717,7 +717,7 @@ class BlueprintTestCase(FlaskTestCase):
             return isinstance(value, bool)
         app.register_blueprint(bp, url_prefix='/py')
         rv = app.test_client().get('/')
-        self.assert_true(b'Success!' in rv.data)
+        self.assert_in(b'Success!', rv.data)
 
     def test_add_template_test_with_template(self):
         bp = flask.Blueprint('bp', __name__)
@@ -730,7 +730,7 @@ class BlueprintTestCase(FlaskTestCase):
         def index():
             return flask.render_template('template_test.html', value=False)
         rv = app.test_client().get('/')
-        self.assert_true(b'Success!' in rv.data)
+        self.assert_in(b'Success!', rv.data)
 
     def test_template_test_with_name_and_template(self):
         bp = flask.Blueprint('bp', __name__)
@@ -743,7 +743,7 @@ class BlueprintTestCase(FlaskTestCase):
         def index():
             return flask.render_template('template_test.html', value=False)
         rv = app.test_client().get('/')
-        self.assert_true(b'Success!' in rv.data)
+        self.assert_in(b'Success!', rv.data)
 
     def test_add_template_test_with_name_and_template(self):
         bp = flask.Blueprint('bp', __name__)
@@ -756,7 +756,7 @@ class BlueprintTestCase(FlaskTestCase):
         def index():
             return flask.render_template('template_test.html', value=False)
         rv = app.test_client().get('/')
-        self.assert_true(b'Success!' in rv.data)
+        self.assert_in(b'Success!', rv.data)
 
 def suite():
     suite = unittest.TestSuite()
diff --git a/flask/testsuite/config.py b/flask/testsuite/config.py
index 6633c6ba..8aaf5285 100644
--- a/flask/testsuite/config.py
+++ b/flask/testsuite/config.py
@@ -28,7 +28,7 @@ class ConfigTestCase(FlaskTestCase):
     def common_object_test(self, app):
         self.assert_equal(app.secret_key, 'devkey')
         self.assert_equal(app.config['TEST_KEY'], 'foo')
-        self.assert_true('ConfigTestCase' not in app.config)
+        self.assert_not_in('ConfigTestCase', app.config)
 
     def test_config_from_file(self):
         app = flask.Flask(__name__)
@@ -141,7 +141,7 @@ class InstanceTestCase(FlaskTestCase):
         try:
             flask.Flask(__name__, instance_path='instance')
         except ValueError as e:
-            self.assert_true('must be absolute' in str(e))
+            self.assert_in('must be absolute', str(e))
         else:
             self.fail('Expected value error')
 
diff --git a/flask/testsuite/ext.py b/flask/testsuite/ext.py
index a6d1be9d..04226181 100644
--- a/flask/testsuite/ext.py
+++ b/flask/testsuite/ext.py
@@ -42,7 +42,7 @@ class ExtImportHookTestCase(FlaskTestCase):
     def teardown(self):
         from flask import ext
         for key in ext.__dict__:
-            self.assert_true('.' not in key)
+            self.assert_not_in('.', key)
 
     def test_flaskext_new_simple_import_normal(self):
         from flask.ext.newext_simple import ext_id
@@ -113,7 +113,7 @@ class ExtImportHookTestCase(FlaskTestCase):
             self.assert_true(tb.tb_frame.f_globals is globals())
 
             next = tb.tb_next
-            self.assert_true('flask_broken/__init__.py' in next.tb_frame.f_code.co_filename)
+            self.assert_in('flask_broken/__init__.py', next.tb_frame.f_code.co_filename)
 
 
 def suite():
diff --git a/flask/testsuite/helpers.py b/flask/testsuite/helpers.py
index 702ab517..b76d36d1 100644
--- a/flask/testsuite/helpers.py
+++ b/flask/testsuite/helpers.py
@@ -48,8 +48,8 @@ class JSONTestCase(FlaskTestCase):
         rv = c.post('/json', data='malformed', content_type='application/json')
         self.assert_equal(rv.status_code, 400)
         self.assert_equal(rv.mimetype, 'application/json')
-        self.assert_true('description' in flask.json.loads(rv.data))
-        self.assert_true('<p>' not in flask.json.loads(rv.data)['description'])
+        self.assert_in('description', flask.json.loads(rv.data))
+        self.assert_not_in('<p>', flask.json.loads(rv.data)['description'])
 
     def test_json_body_encoding(self):
         app = flask.Flask(__name__)
@@ -178,7 +178,7 @@ class SendfileTestCase(FlaskTestCase):
         with app.test_request_context():
             rv = flask.send_file('static/index.html')
             self.assert_true(rv.direct_passthrough)
-            self.assert_true('x-sendfile' in rv.headers)
+            self.assert_in('x-sendfile', rv.headers)
             self.assert_equal(rv.headers['x-sendfile'],
                 os.path.join(app.root_path, 'static/index.html'))
             self.assert_equal(rv.mimetype, 'text/html')
@@ -201,7 +201,7 @@ class SendfileTestCase(FlaskTestCase):
                 f = open(os.path.join(app.root_path, 'static/index.html'))
                 rv = flask.send_file(f)
                 self.assert_equal(rv.mimetype, 'text/html')
-                self.assert_true('x-sendfile' in rv.headers)
+                self.assert_in('x-sendfile', rv.headers)
                 self.assert_equal(rv.headers['x-sendfile'],
                     os.path.join(app.root_path, 'static/index.html'))
             # mimetypes + etag
@@ -229,7 +229,7 @@ class SendfileTestCase(FlaskTestCase):
             with app.test_request_context():
                 f = StringIO('Test')
                 rv = flask.send_file(f)
-                self.assert_true('x-sendfile' not in rv.headers)
+                self.assert_not_in('x-sendfile', rv.headers)
             # etags
             self.assert_equal(len(captured), 1)
 
@@ -325,10 +325,10 @@ class LoggingTestCase(FlaskTestCase):
             with catch_stderr() as err:
                 c.get('/')
                 out = err.getvalue()
-                self.assert_true('WARNING in helpers [' in out)
-                self.assert_true(os.path.basename(__file__.rsplit('.', 1)[0] + '.py') in out)
-                self.assert_true('the standard library is dead' in out)
-                self.assert_true('this is a debug statement' in out)
+                self.assert_in('WARNING in helpers [', out)
+                self.assert_in(os.path.basename(__file__.rsplit('.', 1)[0] + '.py'), out)
+                self.assert_in('the standard library is dead', out)
+                self.assert_in('this is a debug statement', out)
 
             with catch_stderr() as err:
                 try:
@@ -357,13 +357,13 @@ class LoggingTestCase(FlaskTestCase):
 
         rv = app.test_client().get('/')
         self.assert_equal(rv.status_code, 500)
-        self.assert_true(b'Internal Server Error' in rv.data)
+        self.assert_in(b'Internal Server Error', rv.data)
 
         err = out.getvalue()
-        self.assert_true('Exception on / [GET]' in err)
-        self.assert_true('Traceback (most recent call last):' in err)
-        self.assert_true('1/0' in err)
-        self.assert_true('ZeroDivisionError:' in err)
+        self.assert_in('Exception on / [GET]', err)
+        self.assert_in('Traceback (most recent call last):', err)
+        self.assert_in('1/0', err)
+        self.assert_in('ZeroDivisionError:', err)
 
     def test_processor_exceptions(self):
         app = flask.Flask(__name__)
diff --git a/flask/testsuite/subclassing.py b/flask/testsuite/subclassing.py
index a3cf5d0e..dbfdd499 100644
--- a/flask/testsuite/subclassing.py
+++ b/flask/testsuite/subclassing.py
@@ -34,7 +34,7 @@ class FlaskSubclassingTestCase(FlaskTestCase):
 
         rv = app.test_client().get('/')
         self.assert_equal(rv.status_code, 500)
-        self.assert_true(b'Internal Server Error' in rv.data)
+        self.assert_in(b'Internal Server Error', rv.data)
 
         err = out.getvalue()
         self.assert_equal(err, '')
diff --git a/flask/testsuite/templating.py b/flask/testsuite/templating.py
index 08a54d06..b2870dea 100644
--- a/flask/testsuite/templating.py
+++ b/flask/testsuite/templating.py
@@ -99,7 +99,7 @@ class TemplatingTestCase(FlaskTestCase):
         @app.template_filter()
         def my_reverse(s):
             return s[::-1]
-        self.assert_true('my_reverse' in app.jinja_env.filters.keys())
+        self.assert_in('my_reverse', app.jinja_env.filters.keys())
         self.assert_equal(app.jinja_env.filters['my_reverse'], my_reverse)
         self.assert_equal(app.jinja_env.filters['my_reverse']('abcd'), 'dcba')
 
@@ -108,7 +108,7 @@ class TemplatingTestCase(FlaskTestCase):
         def my_reverse(s):
             return s[::-1]
         app.add_template_filter(my_reverse)
-        self.assert_true('my_reverse' in app.jinja_env.filters.keys())
+        self.assert_in('my_reverse', app.jinja_env.filters.keys())
         self.assert_equal(app.jinja_env.filters['my_reverse'], my_reverse)
         self.assert_equal(app.jinja_env.filters['my_reverse']('abcd'), 'dcba')
 
@@ -117,7 +117,7 @@ class TemplatingTestCase(FlaskTestCase):
         @app.template_filter('strrev')
         def my_reverse(s):
             return s[::-1]
-        self.assert_true('strrev' in app.jinja_env.filters.keys())
+        self.assert_in('strrev', app.jinja_env.filters.keys())
         self.assert_equal(app.jinja_env.filters['strrev'], my_reverse)
         self.assert_equal(app.jinja_env.filters['strrev']('abcd'), 'dcba')
 
@@ -126,7 +126,7 @@ class TemplatingTestCase(FlaskTestCase):
         def my_reverse(s):
             return s[::-1]
         app.add_template_filter(my_reverse, 'strrev')
-        self.assert_true('strrev' in app.jinja_env.filters.keys())
+        self.assert_in('strrev', app.jinja_env.filters.keys())
         self.assert_equal(app.jinja_env.filters['strrev'], my_reverse)
         self.assert_equal(app.jinja_env.filters['strrev']('abcd'), 'dcba')
 
@@ -179,7 +179,7 @@ class TemplatingTestCase(FlaskTestCase):
         @app.template_test()
         def boolean(value):
             return isinstance(value, bool)
-        self.assert_true('boolean' in app.jinja_env.tests.keys())
+        self.assert_in('boolean', app.jinja_env.tests.keys())
         self.assert_equal(app.jinja_env.tests['boolean'], boolean)
         self.assert_true(app.jinja_env.tests['boolean'](False))
 
@@ -188,7 +188,7 @@ class TemplatingTestCase(FlaskTestCase):
         def boolean(value):
             return isinstance(value, bool)
         app.add_template_test(boolean)
-        self.assert_true('boolean' in app.jinja_env.tests.keys())
+        self.assert_in('boolean', app.jinja_env.tests.keys())
         self.assert_equal(app.jinja_env.tests['boolean'], boolean)
         self.assert_true(app.jinja_env.tests['boolean'](False))
 
@@ -197,7 +197,7 @@ class TemplatingTestCase(FlaskTestCase):
         @app.template_test('boolean')
         def is_boolean(value):
             return isinstance(value, bool)
-        self.assert_true('boolean' in app.jinja_env.tests.keys())
+        self.assert_in('boolean', app.jinja_env.tests.keys())
         self.assert_equal(app.jinja_env.tests['boolean'], is_boolean)
         self.assert_true(app.jinja_env.tests['boolean'](False))
 
@@ -206,7 +206,7 @@ class TemplatingTestCase(FlaskTestCase):
         def is_boolean(value):
             return isinstance(value, bool)
         app.add_template_test(is_boolean, 'boolean')
-        self.assert_true('boolean' in app.jinja_env.tests.keys())
+        self.assert_in('boolean', app.jinja_env.tests.keys())
         self.assert_equal(app.jinja_env.tests['boolean'], is_boolean)
         self.assert_true(app.jinja_env.tests['boolean'](False))
 
@@ -219,7 +219,7 @@ class TemplatingTestCase(FlaskTestCase):
         def index():
             return flask.render_template('template_test.html', value=False)
         rv = app.test_client().get('/')
-        self.assert_true(b'Success!' in rv.data)
+        self.assert_in(b'Success!', rv.data)
 
     def test_add_template_test_with_template(self):
         app = flask.Flask(__name__)
@@ -230,7 +230,7 @@ class TemplatingTestCase(FlaskTestCase):
         def index():
             return flask.render_template('template_test.html', value=False)
         rv = app.test_client().get('/')
-        self.assert_true(b'Success!' in rv.data)
+        self.assert_in(b'Success!', rv.data)
 
     def test_template_test_with_name_and_template(self):
         app = flask.Flask(__name__)
@@ -241,7 +241,7 @@ class TemplatingTestCase(FlaskTestCase):
         def index():
             return flask.render_template('template_test.html', value=False)
         rv = app.test_client().get('/')
-        self.assert_true(b'Success!' in rv.data)
+        self.assert_in(b'Success!', rv.data)
 
     def test_add_template_test_with_name_and_template(self):
         app = flask.Flask(__name__)
@@ -252,14 +252,14 @@ class TemplatingTestCase(FlaskTestCase):
         def index():
             return flask.render_template('template_test.html', value=False)
         rv = app.test_client().get('/')
-        self.assert_true(b'Success!' in rv.data)
+        self.assert_in(b'Success!', rv.data)
 
     def test_add_template_global(self):
         app = flask.Flask(__name__)
         @app.template_global()
         def get_stuff():
             return 42
-        self.assert_true('get_stuff' in app.jinja_env.globals.keys())
+        self.assert_in('get_stuff', app.jinja_env.globals.keys())
         self.assert_equal(app.jinja_env.globals['get_stuff'], get_stuff)
         self.assert_true(app.jinja_env.globals['get_stuff'](), 42)
         with app.app_context():
diff --git a/flask/testsuite/testing.py b/flask/testsuite/testing.py
index 2e735c47..a60109e1 100644
--- a/flask/testsuite/testing.py
+++ b/flask/testsuite/testing.py
@@ -106,7 +106,7 @@ class TestToolsTestCase(FlaskTestCase):
                 with c.session_transaction() as sess:
                     pass
             except RuntimeError as e:
-                self.assert_true('Session backend did not open a session' in str(e))
+                self.assert_in('Session backend did not open a session', str(e))
             else:
                 self.fail('Expected runtime error')
 
@@ -130,7 +130,7 @@ class TestToolsTestCase(FlaskTestCase):
             with c.session_transaction() as s:
                 pass
         except RuntimeError as e:
-            self.assert_true('cookies' in str(e))
+            self.assert_in('cookies', str(e))
         else:
             self.fail('Expected runtime error')
 
@@ -153,7 +153,7 @@ class TestToolsTestCase(FlaskTestCase):
 
             resp = c.get('/other')
             self.assert_true(not hasattr(flask.g, 'value'))
-            self.assert_true(b'Internal Server Error' in resp.data)
+            self.assert_in(b'Internal Server Error', resp.data)
             self.assert_equal(resp.status_code, 500)
             flask.g.value = 23