Flask: Testing render_template()

[nueverest]

How do I test this line?
return render_template(u'http_error.html', error_detail=detail)

I am a beginner as far as flask testing is concerned.

Could you document the answer to this on your testing page? http://flask.pocoo.org/docs/testing/

There is an unanswered question similar to this on stackoverflow.
http://stackoverflow.com/questions/23987564/test-flask-render-template-context

[mitsuhiko]

Please do not use the bug tracker as support forum :) Not sure what there is to test about template rendering. There are examples for testing general responses on the testing page you linked.

[nueverest]

I'm requesting that your documentation contain a feature that will help me and others test their code. It says on your site, "Something that is untested is broken."

The Issue I am raising is that a heavily used method render_template() does not appear to be fully testable in a direct sort of manner, and could use more documentation.

It is a little strange that I need to use get() to test render_template(). This leads to implicit rather than explicit testing of render_template(). If I use get() and discover that something isn't showing up, then I'm probably not using render_template() correctly or my template doesn't display the data correctly or I may have a database error.

I can write tests that check the database call and eliminate it as the source of the error. Why can't I do the same with render_template(), and narrow it down to the template itself?

I'm assuming that this is possible, but undocumented. Thus my request that it be documented.

This raises another question: Can I test whether the render_template is providing the template with the correct parameters? e.g. The template expects a variable 'dog', but render template provides 'octopus'. Is there an automated way to test this?

[ThiefMaster]

Why would you write unit tests in your application to test core framework functionality?

Anyway, maybe the template_rendered signal is helpful for you.

[DasIch]

You shouldn't test that render_template() works because you shouldn't test how your application is implemented.

Tests exist to precisely and formally define what your application does and they do so by making sure that _using_ the application produces the results you expect it to.

The fact that a web application even uses a database or templates is an implementation detail and completely irrelevant for the tests.

For that reason the documentation does not contain any information on how to do such a thing nor will it be included.

[JohnVonNeumann]

@DasIch Didn't quite get your comment first read through (my misunderstanding of testing), but cheers, great explanation.