Use pytest.raises() instead of try/catch with asser 0

This is somehow more readable, and enable using the features of pytest's ExeptionInfo (such as errisinstance).

tests/test_blueprints.py

@@ -174,12 +174,9 @@ def test_templates_and_static(test_apps):
         assert flask.url_for('admin.static', filename='test.txt') == '/admin/static/test.txt'
 
     with app.test_request_context():
-        try:
+        with pytest.raises(TemplateNotFound) as e:
             flask.render_template('missing.html')
-        except TemplateNotFound as e:
-            assert e.name == 'missing.html'
-        else:
-            assert 0, 'expected exception'
+        assert e.value.name == 'missing.html'
 
     with flask.Flask(__name__).test_request_context():
         assert flask.render_template('nested/nested.txt') == 'I\'m nested'