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).

Author: R-Peleg

tests/test_basic.py

@@ -307,12 +307,8 @@ def test_missing_session():
     app = flask.Flask(__name__)
 
     def expect_exception(f, *args, **kwargs):
-        try:
-            f(*args, **kwargs)
-        except RuntimeError as e:
-            assert e.args and 'session is unavailable' in e.args[0]
-        else:
-            assert False, 'expected exception'
+        e = pytest.raises(RuntimeError, f, *args, **kwargs)
+        assert e.value.args and 'session is unavailable' in e.value.args[0]
     with app.test_request_context():
         assert flask.session.get('missing_key') is None
         expect_exception(flask.session.__setitem__, 'foo', 42)
@@ -853,12 +849,9 @@ def fail():
 
     app.config['TRAP_BAD_REQUEST_ERRORS'] = True
     c = app.test_client()
-    try:
-        c.get('/fail')
-    except KeyError as e:
-        assert isinstance(e, BadRequest)
-    else:
-        assert False, 'Expected exception'
+    with pytest.raises(KeyError) as e:
+        c.get("/fail")
+    assert e.errisinstance(BadRequest)
 
 
 def test_trapping_of_all_http_exceptions():
@@ -888,13 +881,10 @@ def index():
     # stack otherwise and we want to ensure that this is not the case
     # to not negatively affect other tests.
     with app.test_client() as c:
-        try:
+        with pytest.raises(DebugFilesKeyError) as e:
             c.post('/fail', data={'foo': 'index.txt'})
-        except DebugFilesKeyError as e:
-            assert 'no file contents were transmitted' in str(e)
-            assert 'This was submitted: "index.txt"' in str(e)
-        else:
-            assert False, 'Expected exception'
+        assert 'no file contents were transmitted' in str(e.value)
+        assert 'This was submitted: "index.txt"' in str(e.value)
 
 
 def test_response_creation():
@@ -1203,12 +1193,8 @@ def index():
         c = app.test_client()
         if config_key is not None:
             app.config[config_key] = True
-            try:
+            with pytest.raises(Exception):
                 c.get('/')
-            except Exception:
-                pass
-            else:
-                assert False, 'expected exception'
         else:
             assert c.get('/').status_code == 500
 
@@ -1345,14 +1331,11 @@ def index():
         return 'Awesome'
     assert not app.got_first_request
     assert app.test_client().get('/').data == b'Awesome'
-    try:
+    with pytest.raises(AssertionError) as e:
         @app.route('/foo')
         def broken():
             return 'Meh'
-    except AssertionError as e:
-        assert 'A setup function was called' in str(e)
-    else:
-        assert False, 'Expected exception'
+    assert 'A setup function was called' in str(e)
 
     app.debug = False
 
@@ -1408,14 +1391,11 @@ def test_routing_redirect_debugging():
     def foo():
         return 'success'
     with app.test_client() as c:
-        try:
+        with pytest.raises(AssertionError) as e:
             c.post('/foo', data={})
-        except AssertionError as e:
-            assert 'http://localhost/foo/' in str(e)
-            assert ('Make sure to directly send '
-                    'your POST-request to this URL') in str(e)
-        else:
-            assert False, 'Expected exception'
+        assert 'http://localhost/foo/' in str(e)
+        assert ('Make sure to directly send '
+                'your POST-request to this URL') in str(e)
 
         rv = c.get('/foo', data={}, follow_redirects=True)
         assert rv.data == b'success'

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'

tests/test_config.py

@@ -89,12 +89,9 @@ def test_config_from_envvar():
     try:
         os.environ = {}
         app = flask.Flask(__name__)
-        try:
+        with pytest.raises(RuntimeError) as e:
             app.config.from_envvar('FOO_SETTINGS')
-        except RuntimeError as e:
-            assert "'FOO_SETTINGS' is not set" in str(e)
-        else:
-            assert 0, 'expected exception'
+        assert "'FOO_SETTINGS' is not set" in str(e.value)
         assert not app.config.from_envvar('FOO_SETTINGS', silent=True)
 
         os.environ = {'FOO_SETTINGS': __file__.rsplit('.', 1)[0] + '.py'}
@@ -108,46 +105,37 @@ def test_config_from_envvar_missing():
     env = os.environ
     try:
         os.environ = {'FOO_SETTINGS': 'missing.cfg'}
-        try:
+        with pytest.raises(IOError) as e:
             app = flask.Flask(__name__)
             app.config.from_envvar('FOO_SETTINGS')
-        except IOError as e:
-            msg = str(e)
-            assert msg.startswith('[Errno 2] Unable to load configuration '
-                                  'file (No such file or directory):')
-            assert msg.endswith("missing.cfg'")
-        else:
-            assert False, 'expected IOError'
+        msg = str(e.value)
+        assert msg.startswith('[Errno 2] Unable to load configuration '
+                              'file (No such file or directory):')
+        assert msg.endswith("missing.cfg'")
         assert not app.config.from_envvar('FOO_SETTINGS', silent=True)
     finally:
         os.environ = env
 
 
 def test_config_missing():
     app = flask.Flask(__name__)
-    try:
+    with pytest.raises(IOError) as e:
         app.config.from_pyfile('missing.cfg')
-    except IOError as e:
-        msg = str(e)
-        assert msg.startswith('[Errno 2] Unable to load configuration '
-                              'file (No such file or directory):')
-        assert msg.endswith("missing.cfg'")
-    else:
-        assert 0, 'expected config'
+    msg = str(e.value)
+    assert msg.startswith('[Errno 2] Unable to load configuration '
+                          'file (No such file or directory):')
+    assert msg.endswith("missing.cfg'")
     assert not app.config.from_pyfile('missing.cfg', silent=True)
 
 
 def test_config_missing_json():
     app = flask.Flask(__name__)
-    try:
+    with pytest.raises(IOError) as e:
         app.config.from_json('missing.json')
-    except IOError as e:
-        msg = str(e)
-        assert msg.startswith('[Errno 2] Unable to load configuration '
-                              'file (No such file or directory):')
-        assert msg.endswith("missing.json'")
-    else:
-        assert 0, 'expected config'
+    msg = str(e.value)
+    assert msg.startswith('[Errno 2] Unable to load configuration '
+                          'file (No such file or directory):')
+    assert msg.endswith("missing.json'")
     assert not app.config.from_json('missing.json', silent=True)
 
 

tests/test_reqctx.py

@@ -140,12 +140,8 @@ def index():
     ctx.push()
     assert index() == 'Hello World!'
     ctx.pop()
-    try:
+    with pytest.raises(RuntimeError):
         index()
-    except RuntimeError:
-        pass
-    else:
-        assert 0, 'expected runtime error'
 
 @pytest.mark.skipif(greenlet is None, reason='greenlet not installed')
 def test_greenlet_context_copying():

tests/test_testing.py

@@ -100,13 +100,10 @@ def test_session_transactions_no_null_sessions():
     app.testing = True
 
     with app.test_client() as c:
-        try:
+        with pytest.raises(RuntimeError) as e:
             with c.session_transaction() as sess:
                 pass
-        except RuntimeError as e:
-            assert 'Session backend did not open a session' in str(e)
-        else:
-            assert False, 'Expected runtime error'
+        assert 'Session backend did not open a session' in str(e.value)
 
 def test_session_transactions_keep_context():
     app = flask.Flask(__name__)
@@ -124,13 +121,10 @@ def test_session_transaction_needs_cookies():
     app = flask.Flask(__name__)
     app.testing = True
     c = app.test_client(use_cookies=False)
-    try:
+    with pytest.raises(RuntimeError) as e:
         with c.session_transaction() as s:
             pass
-    except RuntimeError as e:
-        assert 'cookies' in str(e)
-    else:
-        assert False, 'Expected runtime error'
+    assert 'cookies' in str(e.value)
 
 def test_test_client_context_binding():
     app = flask.Flask(__name__)