diff --git a/.circleci/config.yml b/.circleci/config.yml
index b3b8a70..cb78e72 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -40,9 +40,9 @@ jobs:
       # Download and cache dependencies
       - restore_cache:
           keys:
-            - v3-dependencies-{{ checksum "Pipfile.lock" }}
+            - v4-dependencies-{{ checksum "Pipfile.lock" }}
             # fallback to using the latest cache if no exact match is found
-            - v3-dependencies-
+            - v4-dependencies-
 
       - run:
           name: install dependencies
@@ -54,13 +54,18 @@ jobs:
       - save_cache:
           paths:
             - ./.venv
-          key: v3-dependencies-{{ checksum "Pipfile.lock" }}
+          key: v4-dependencies-{{ checksum "Pipfile.lock" }}
 
       - run:
           name: run tests
           command: |
             make tests
 
+      - run:
+          name: run tests for the singlefile example
+          command: |
+            cd examples/singlefile && pipenv run python -m unittest app.py
+
   release:
     <<: *defaults
 
@@ -69,9 +74,9 @@ jobs:
 
       - restore_cache:
           keys:
-            - v3-dependencies-{{ checksum "Pipfile.lock" }}
+            - v4-dependencies-{{ checksum "Pipfile.lock" }}
             # fallback to using the latest cache if no exact match is found
-            - v3-dependencies-
+            - v4-dependencies-
 
       - run:
           name: install dependencies
@@ -84,7 +89,7 @@ jobs:
       - save_cache:
           paths:
             - ./.venv
-          key: v3-dependencies-{{ checksum "Pipfile.lock" }}
+          key: v4-dependencies-{{ checksum "Pipfile.lock" }}
 
       - run:
           name: verify git tag vs. version
diff --git a/Pipfile b/Pipfile
index abbfc46..a583929 100644
--- a/Pipfile
+++ b/Pipfile
@@ -32,6 +32,7 @@ pytest = "*"
 pytest-cov = "*"
 pytest-randomly = "*"
 twine = "*"
+webtest = "*"
 
 [packages]
 "pyramid-openapi3" = {editable = true, path = "."}
diff --git a/Pipfile.lock b/Pipfile.lock
index 4b8ed02..4047837 100644
--- a/Pipfile.lock
+++ b/Pipfile.lock
@@ -1,7 +1,7 @@
 {
     "_meta": {
         "hash": {
-            "sha256": "3b7a82e18c9037ba964526ec25124982f12313de0ea12991938f945b237b0ee4"
+            "sha256": "43afbd3061dfa163e466f8b0cc6e5caddeb804406331beeb28fe19bf5f988856"
         },
         "pipfile-spec": 6,
         "requires": {},
@@ -28,13 +28,6 @@
             ],
             "version": "==1.6.1"
         },
-        "importlib-resources": {
-            "hashes": [
-                "sha256:6e2783b2538bd5a14678284a3962b0660c715e5a0f10243fd5e00a4b5974f50b",
-                "sha256:d3279fd0f6f847cced9f7acc19bd3e5df54d34f93a2e7bb5f238f81545787078"
-            ],
-            "version": "==1.0.2"
-        },
         "jsonschema": {
             "hashes": [
                 "sha256:000e68abd33c972a5248544925a0cae7d1125f9bf6c58280d37546b946769a08",
@@ -114,17 +107,17 @@
         },
         "plaster-pastedeploy": {
             "hashes": [
-                "sha256:71e29b0ab90df8343bca5f0debe4706f0f8147308a78922c8c26e8252809bce4",
-                "sha256:c231130cb86ae414084008fe1d1797db7e61dc5eaafb5e755de21387c27c6fae"
+                "sha256:391d93a4e1ff81fc3bae27508ebb765b61f1724ae6169f83577f06b6357be7fd",
+                "sha256:7c8aa37c917b615c70bf942b24dc1e0455c49f62f1a2214b1a0dd98871644bbb"
             ],
-            "version": "==0.6"
+            "version": "==0.7"
         },
         "pyramid": {
             "hashes": [
-                "sha256:1b2d380a70e5edbc72be3fc5e7b891a0e29b0ec41770712195cdd46ee6d8a13d",
-                "sha256:e70a9bac805284ebe7123fdd412e22a4c1d214603b3a074ac8f1185a0dd7c63e"
+                "sha256:198250687a6f90940572d2eebff6cdf9a6eb9fc6bfd70f84beaa504ea841f861",
+                "sha256:f18f1862ee7224a2d2e3f503277456cfd81a7ca18432e778ea03c25669884c14"
             ],
-            "version": "==1.10.2"
+            "version": "==1.10.3"
         },
         "pyramid-openapi3": {
             "editable": true,
@@ -251,6 +244,14 @@
             ],
             "version": "==19.1.0"
         },
+        "beautifulsoup4": {
+            "hashes": [
+                "sha256:034740f6cb549b4e932ae1ab975581e6103ac8f942200a0e9759065984391858",
+                "sha256:945065979fb8529dd2f37dbb58f00b661bdbcbebf954f93b32fdf5263ef35348",
+                "sha256:ba6d5c59906a85ac23dadfe5c88deaf3e179ef565f4898671253e50a78680718"
+            ],
+            "version": "==4.7.1"
+        },
         "black": {
             "hashes": [
                 "sha256:09a9dcb7c46ed496a9850b76e4e825d6049ecd38b611f1224857a79bd985a8cf",
@@ -512,13 +513,6 @@
             ],
             "version": "==0.9"
         },
-        "importlib-resources": {
-            "hashes": [
-                "sha256:6e2783b2538bd5a14678284a3962b0660c715e5a0f10243fd5e00a4b5974f50b",
-                "sha256:d3279fd0f6f847cced9f7acc19bd3e5df54d34f93a2e7bb5f238f81545787078"
-            ],
-            "version": "==1.0.2"
-        },
         "isort": {
             "hashes": [
                 "sha256:01cb7e1ca5e6c5b3f235f0385057f70558b70d2f00320208825fa62887292f43",
@@ -750,12 +744,19 @@
             ],
             "version": "==1.2.1"
         },
+        "soupsieve": {
+            "hashes": [
+                "sha256:6898e82ecb03772a0d82bd0d0a10c0d6dcc342f77e0701d0ec4a8271be465ece",
+                "sha256:b20eff5e564529711544066d7dc0f7661df41232ae263619dede5059799cdfca"
+            ],
+            "version": "==1.9.1"
+        },
         "testfixtures": {
             "hashes": [
-                "sha256:79b1c1ae5407750406eaf4407ea0d4c0d50b60bec3f85494c6401e072e7d2239",
-                "sha256:fc52e99561141e2e10fd79f3a565502238adcb90f6e2a7634abceef2d2c17bf7"
+                "sha256:6b79324f35852eaacd4f5f440b20ee1b98df23001ff88db8b8bde3746f753f0a",
+                "sha256:c0028d2acd45e6604d359b806132af05815d64e882cf995fa45e6814ddaade13"
             ],
-            "version": "==6.6.2"
+            "version": "==6.7.0"
         },
         "toml": {
             "hashes": [
@@ -825,6 +826,13 @@
             ],
             "version": "==16.4.3"
         },
+        "waitress": {
+            "hashes": [
+                "sha256:c369e238bd81ef7d61f04825f06f107c42094de60d13d8de8e71952c7c683dfe",
+                "sha256:de0dbd36dec695d90ac8e7464998f28c7e968a2dde3c37b06bb0a714df4dad62"
+            ],
+            "version": "==1.2.1"
+        },
         "webencodings": {
             "hashes": [
                 "sha256:a0af1213f3c2226497a97e2b3aa01a7e4bee4f403f95be16fc9acd2947514a78",
@@ -832,6 +840,21 @@
             ],
             "version": "==0.5.1"
         },
+        "webob": {
+            "hashes": [
+                "sha256:05aaab7975e0ee8af2026325d656e5ce14a71f1883c52276181821d6d5bf7086",
+                "sha256:36db8203c67023d68c1b00208a7bf55e3b10de2aa317555740add29c619de12b"
+            ],
+            "version": "==1.8.5"
+        },
+        "webtest": {
+            "hashes": [
+                "sha256:41348efe4323a647a239c31cde84e5e440d726ca4f449859264e538d39037fd0",
+                "sha256:f3a603b8f1dd873b9710cd5a7dd0889cf758d7e1c133b1dae971c04f567e566e"
+            ],
+            "index": "pypi",
+            "version": "==2.0.33"
+        },
         "zipp": {
             "hashes": [
                 "sha256:55ca87266c38af6658b84db8cfb7343cdb0bf275f93c7afaea0d8e7a209c7478",
diff --git a/examples/singlefile/app.py b/examples/singlefile/app.py
new file mode 100644
index 0000000..6ea16ba
--- /dev/null
+++ b/examples/singlefile/app.py
@@ -0,0 +1,150 @@
+"""A single-file demo of pyramid_openapi3.
+
+Usage:
+* git clone https://github.com/niteoweb/pyramid_openapi3.git
+* cd pyramid_openapi3/examples/singlefile
+* virtualenv -p python3.7 .
+* source bin/activate
+* pip install pyramid_openapi3
+* python app.py
+"""
+
+from pyramid.config import Configurator
+from pyramid.httpexceptions import HTTPForbidden
+from pyramid.view import view_config
+from wsgiref.simple_server import make_server
+
+import tempfile
+import unittest
+
+# This is usually in a separate openapi.yaml file, but for the sake of the
+# example we want everything in a single file. Other examples have it nicely
+# separated.
+OPENAPI_DOCUMENT = (
+    b'openapi: "3.0.0"\n'
+    b"info:\n"
+    b'  version: "1.0.0"\n'
+    b"  title: Ping API\n"
+    b"paths:\n"
+    b"  /hello:\n"
+    b"    get:\n"
+    b"      parameters:\n"
+    b"        - name: name\n"
+    b"          in: query\n"
+    b"          required: true\n"
+    b"          schema:\n"
+    b"            type: string\n"
+    b"            minLength: 3\n"
+    b"      responses:\n"
+    b"        200:\n"
+    b"          description: Say hi!\n"
+)
+
+
+@view_config(route_name="hello", renderer="json", request_method="GET", openapi=True)
+def hello(request):
+    """Say hello."""
+    if request.openapi_validated.parameters["query"]["name"] == "admin":
+        raise HTTPForbidden()
+    return {"hello": request.openapi_validated.parameters["query"]["name"]}
+
+
+def app(spec):
+    """Prepare a Pyramid app."""
+    with Configurator() as config:
+        config.include("pyramid_openapi3")
+        config.pyramid_openapi3_spec(spec)
+        config.pyramid_openapi3_add_explorer()
+        config.add_route("hello", "/hello")
+        config.scan(".")
+        return config.make_wsgi_app()
+
+
+if __name__ == "__main__":
+    """If app.py is called directly, start up the app."""
+    with tempfile.NamedTemporaryFile() as document:
+        document.write(OPENAPI_DOCUMENT)
+        document.seek(0)
+
+        print("visit api explorer at http://0.0.0.0:6543/docs/")  # noqa: T001
+        server = make_server("0.0.0.0", 6543, app(document.name))
+        server.serve_forever()
+
+
+#######################################
+#           ---- Tests ----           #
+# A couple of functional tests to     #
+# showcase pyramid_openapi3 features. #
+# Usage: python -m unittest app.py    #
+#######################################
+
+from openapi_core.schema.parameters.exceptions import InvalidParameterValue  # noqa
+from openapi_core.schema.parameters.exceptions import MissingRequiredParameter  # noqa
+from openapi_core.schema.responses.exceptions import InvalidResponse  # noqa
+
+
+class FunctionalTests(unittest.TestCase):
+    """A suite of tests that make actual requests to a running app."""
+
+    def setUp(self):
+        """Start up the app so that tests can send requests to it."""
+        from webtest import TestApp
+
+        with tempfile.NamedTemporaryFile() as document:
+            document.write(OPENAPI_DOCUMENT)
+            document.seek(0)
+
+            self.testapp = TestApp(app(document.name))
+
+    def test_nothing_on_root(self):
+        """We have not configured our app to serve anything on root."""
+        res = self.testapp.get("/", status=404)
+        self.assertIn("404 Not Found", res.text)
+
+    def test_api_explorer_on_docs(self):
+        """Swagger's API Explorer should be served on /docs/."""
+        res = self.testapp.get("/docs/", status=200)
+        self.assertIn("<title>Swagger UI</title>", res.text)
+
+    def test_hello(self):
+        """Say hello."""
+        res = self.testapp.get("/hello?name=john", status=200)
+        self.assertIn('{"hello": "john"}', res.text)
+
+    def test_undefined_response(self):
+        """Saying hello to admin should fail with 403 Forbidden.
+
+        But because we have not defined how a 403 response should look in
+        OPENAPI_DOCUMENT, we instead get a InvalidResponse exception.
+
+        This is to prevent us from forgetting to define all possible responses
+        in our opeanapi document.
+        """
+        try:
+            self.testapp.get("/hello?name=admin", status=200)
+        except InvalidResponse as exc:
+            self.assertEqual(str(exc), "Unknown response http status: 403")
+
+    def test_name_missing(self):
+        """Our view code does not even get called is request is not per-spec.
+
+        We don't have to write (and test!) any validation code in our view!
+        """
+        try:
+            self.testapp.get("/hello", status=200)
+        except MissingRequiredParameter as exc:
+            self.assertEqual(str(exc), "Missing required parameter: name")
+
+    def test_too_short_name(self):
+        """A too short name is picked up by openapi-core validation.
+
+        We don't have to write (and test!) validation any code in our view!
+        """
+        try:
+            self.testapp.get("/hello?name=yo", status=200)
+        except InvalidParameterValue as exc:
+            self.assertEqual(
+                str(exc),
+                "Invalid parameter value for `name`: Value is shorter (2) "
+                "than the minimum length of 3",
+            )
diff --git a/pyramid_openapi3/__init__.py b/pyramid_openapi3/__init__.py
index 5ed857b..5a68e84 100644
--- a/pyramid_openapi3/__init__.py
+++ b/pyramid_openapi3/__init__.py
@@ -59,6 +59,7 @@ def wrapper_view(context, request):
                     )
                 else:
                     # Do the view
+                    request.openapi_validated.raise_for_errors()
                     response = view(context, request)
 
             except HTTPException as exc:
@@ -151,7 +152,6 @@ def spec_view(request):
 
         config.add_route(route_name, route)
         config.add_view(route_name=route_name, view=spec_view)
-        config.add_view(route_name=route_name, view=spec_view)
 
         custom_formatters = config.registry.settings.get("pyramid_openapi3_formatters")