In the method is_text_present (https://github.com/mozilla/remo-tests/pull/41/files#L1R21) you are returning a string, not a boolean (True or False). So you have to assert that the query is contained the string you returned.

I would change is_text_present to this
<code>
@property
def page_text(self, query): 
   return self.find_element(*self._page_source).text 
</code>
And then change the assert above to 
<code>
Assert.contains(query, profile_page.page_text) 
</code>