Using url_for in tests

Question

I am writing some tests for a Flask application and am running into an issue where the URLs in my test_client responses do not match those produced by calling url_for from within the test case. For example, I have the following in my template:

<li><a href="#" onClick="requestReport('{{ url_for('report') }}', '{{ session['email'] }}');">Report</a></li>

The response from the test_client renders this as:

<li><a href="#" onClick="requestReport('/api/report', '[email protected]');">Report</a></li>

I have a test case that checks to make sure this URL appears on a page under certain conditions:

self.client = self.app.test_client(use_cookies=True)
with self.app.app_context():
    page = self.client.get(url_for("index"), follow_redirects=True).data.decode()
    assert url_for("report") in page

The problem is that this test will fail even when the URL appears on the page, because the url_for call in the template is producing different output than the url_for call in my test case. If I print url_for("report") from the test case code, I get:

http://localhost:5000/api/report

I have the SERVER_NAME key in app.config set to "localhost:5000" because if I do not have SERVER_NAME set the test case code will throw this error:

RuntimeError: Application was not able to create a URL adapter for request independent URL generation. You might be able to fix this by setting the SERVER_NAME config variable.

Obviously, I could work around this by hard-coding the URL in my test case code, but I would prefer to use URL_for so that future changes to my URL do not break my test code.

I have tried a couple different strings as SERVER_NAME, including "" which just generates a malformed URL that still doesn't match the one generated in the response.

Is there some way to fix this other than hard-coding the URL?

Answer 1

If you use url_for in an application context like you do in your test code Flask automatically assumes you want to create an external link including the full host name (set in the SERVER_NAME config variable). Whereas the url_for in your template will create an internal link without the host name. So they won't match. To check for equality you need to explicitly set the _external property to False.

self.client = self.app.test_client(use_cookies=True)
with self.app.app_context():
    page = self.client.get(url_for("index"), follow_redirects=True).data.decode()
    assert url_for("report", _external=False) in page

Answer 2

For API testing, you can use test_request_context

class TestFlaskApi(unittest.TestCase):                                          
    def setUp(self):                                                            
        self.app = create_app()                                                 
        self.app_context = self.app.test_request_context()                      
        self.app_context.push()                                                 
        self.client = self.app.test_client() 

    def test_hello(self):                                                       
        response =  self.client.get(url_for('api.hello'),                       
                                    content_type='text')                        

        self.assertEqual(response.get_data(as_text=True), 'hello') 

Answer 3

The top answer pushed the test request context but didn't pop it in tearDown method. The proper setup and teardown should like this:

class TestFlaskApi(unittest.TestCase):
    def setUp(self):
        self.app = create_app()
        self.context = self.app.test_request_context()
        self.context.push()  # push it
        self.client = self.app.test_client()

    def tearDown(self):
        self.context.pop()  # pop it

    def test_hello(self):
        response =  self.client.get(url_for('api.hello'), content_type='text')
        self.assertEqual(response.get_data(as_text=True), 'hello')

If you are using pytest, check out this answer.