Testing WSGI Applications

Test Client

Werkzeug provides a Client to simulate requests to a WSGI application without starting a server. The client has methods for making different types of requests, as well as managing cookies across requests.

>>> from werkzeug.test import Client
>>> from werkzeug.testapp import test_app
>>> c = Client(test_app)
>>> response = c.get("/")
>>> response.status_code
>>> response.headers
Headers([('Content-Type', 'text/html; charset=utf-8'), ('Content-Length', '5211')])
>>> response.get_data(as_text=True)
'<!doctype html>...'

The client’s request methods return instances of TestResponse. This provides extra attributes and methods on top of Response that are useful for testing.

Request Body

By passing a dict to data, the client will construct a request body with file and form data. It will set the content type to application/x-www-form-urlencoded if there are no files, or multipart/form-data there are.

import io

response = client.post(data={
    "name": "test",
    "file": (BytesIO("file contents".encode("utf8")), "test.txt")

Pass a string, bytes, or file-like object to data to use that as the raw request body. In that case, you should set the content type appropriately. For example, to post YAML:

response = client.post(
    data="a: value\nb: 1\n", content_type="application/yaml"

A shortcut when testing JSON APIs is to pass a dict to json instead of using data. This will automatically call json.dumps() and set the content type to application/json. Additionally, if the app returns JSON, response.json will automatically call json.loads().

response = client.post("/api", json={"a": "value", "b": 1})
obj = response.json()

Environment Builder

EnvironBuilder is used to construct a WSGI environ dict. The test client uses this internally to prepare its requests. The arguments passed to the client request methods are the same as the builder.

Sometimes, it can be useful to construct a WSGI environment manually. An environ builder or dict can be passed to the test client request methods in place of other arguments to use a custom environ.

from werkzeug.test import EnvironBuilder
builder = EnvironBuilder(...)
# build an environ dict
environ = builder.get_environ()
# build an environ dict wrapped in a request
request = builder.get_request()

The test client responses make this available through TestResponse.request and response.request.environ.


class werkzeug.test.Client(application, response_wrapper=None, use_cookies=True, allow_subdomain_redirects=False)

Simulate sending requests to a WSGI application without running a WSGI or HTTP server.

  • application (WSGIApplication) – The WSGI application to make requests to.

  • response_wrapper (type[Response] | None) – A Response class to wrap response data with. Defaults to TestResponse. If it’s not a subclass of TestResponse, one will be created.

  • use_cookies (bool) – Persist cookies from Set-Cookie response headers to the Cookie header in subsequent requests. Domain and path matching is supported, but other cookie parameters are ignored.

  • allow_subdomain_redirects (bool) – Allow requests to follow redirects to subdomains. Enable this if the application handles subdomains and redirects between them.


Changed in version 2.3: Simplify cookie implementation, support domain and path matching.

Changed in version 2.1: All data is available as properties on the returned response object. The response cannot be returned as a tuple.

Changed in version 2.0: response_wrapper is always a subclass of :class:TestResponse.

Changed in version 0.5: Added the use_cookies parameter.

Return a Cookie if it exists. Cookies are uniquely identified by (domain, path, key).

  • key (str) – The decoded form of the key for the cookie.

  • domain (str) – The domain the cookie was set for.

  • path (str) – The path the cookie was set for.

Return type:

Cookie | None


Added in version 2.3.

Set a cookie to be sent in subsequent requests.

This is a convenience to skip making a test request to a route that would set the cookie. To test the cookie, make a test request to a route that uses the cookie value.

The client uses domain, origin_only, and path to determine which cookies to send with a request. It does not use other cookie parameters that browsers use, since they’re not applicable in tests.

  • key (str) – The key part of the cookie.

  • value (str) – The value part of the cookie.

  • domain (str) – Send this cookie with requests that match this domain. If origin_only is true, it must be an exact match, otherwise it may be a suffix match.

  • origin_only (bool) – Whether the domain must be an exact match to the request.

  • path (str) – Send this cookie with requests that match this path either exactly or as a prefix.

  • kwargs (Any) – Passed to dump_cookie().

Return type:


Changed in version 3.0: The parameter server_name is removed. The first parameter is key. Use the domain and origin_only parameters instead.


Changed in version 2.3: The origin_only parameter was added.

Changed in version 2.3: The domain parameter defaults to localhost.

Delete a cookie if it exists. Cookies are uniquely identified by (domain, path, key).

  • key (str) – The decoded form of the key for the cookie.

  • domain (str) – The domain the cookie was set for.

  • path (str) – The path the cookie was set for.

Return type:


Changed in version 3.0: The server_name parameter is removed. The first parameter is key. Use the domain parameter instead.

Changed in version 3.0: The secure, httponly and samesite parameters are removed.


Changed in version 2.3: The domain parameter defaults to localhost.

open(*args, buffered=False, follow_redirects=False, **kwargs)

Generate an environ dict from the given arguments, make a request to the application using it, and return the response.

  • args (Any) – Passed to EnvironBuilder to create the environ for the request. If a single arg is passed, it can be an existing EnvironBuilder or an environ dict.

  • buffered (bool) – Convert the iterator returned by the app into a list. If the iterator has a close() method, it is called automatically.

  • follow_redirects (bool) – Make additional requests to follow HTTP redirects until a non-redirect status is returned. TestResponse.history lists the intermediate responses.

  • kwargs (Any)

Return type:



Changed in version 2.1: Removed the as_tuple parameter.

Changed in version 2.0: The request input stream is closed when calling response.close(). Input streams for redirects are automatically closed.

Changed in version 0.5: If a dict is provided as file in the dict for the data parameter the content type has to be called content_type instead of mimetype. This change was made for consistency with werkzeug.FileWrapper.

Changed in version 0.5: Added the follow_redirects parameter.

get(*args, **kw)

Call open() with method set to GET.

Return type:


post(*args, **kw)

Call open() with method set to POST.

Return type:


put(*args, **kw)

Call open() with method set to PUT.

Return type:


delete(*args, **kw)

Call open() with method set to DELETE.

Return type:


patch(*args, **kw)

Call open() with method set to PATCH.

Return type:


options(*args, **kw)

Call open() with method set to OPTIONS.

Return type:


head(*args, **kw)

Call open() with method set to HEAD.

Return type:


trace(*args, **kw)

Call open() with method set to TRACE.

Return type:


class werkzeug.test.TestResponse(response, status, headers, request, history=(), **kwargs)

Response subclass that provides extra information about requests made with the test Client.

Test client requests will always return an instance of this class. If a custom response class is passed to the client, it is subclassed along with this to support test information.

If the test request included large files, or if the application is serving a file, call close() to close any open files and prevent Python showing a ResourceWarning.


Changed in version 2.2: Set the default_mimetype to None to prevent a mimetype being assumed if missing.

Changed in version 2.1: Response instances cannot be treated as tuples.

Added in version 2.0: Test client methods always return instances of this class.

default_mimetype: str | None = None

the default mimetype if none is provided.

request: Request

A request object with the environ used to make the request that resulted in this response.

history: tuple[TestResponse, ...]

A list of intermediate responses. Populated when the test request is made with follow_redirects enabled.

property text: str

The response data as text. A shortcut for response.get_data(as_text=True).


Added in version 2.1.

class werkzeug.test.Cookie(key, value, decoded_key, decoded_value, expires, max_age, domain, origin_only, path, secure, http_only, same_site)

A cookie key, value, and parameters.

The class itself is not a public API. Its attributes are documented for inspection with Client.get_cookie() only.


Added in version 2.3.

key: str

The cookie key, encoded as a client would see it.

value: str

The cookie key, encoded as a client would see it.

decoded_key: str

The cookie key, decoded as the application would set and see it.

decoded_value: str

The cookie value, decoded as the application would set and see it.

expires: datetime | None

The time at which the cookie is no longer valid.

max_age: int | None

The number of seconds from when the cookie was set at which it is no longer valid.

domain: str

The domain that the cookie was set for, or the request domain if not set.

origin_only: bool

Whether the cookie will be sent for exact domain matches only. This is True if the Domain parameter was not present.

path: str

The path that the cookie was set for.

secure: bool | None

The Secure parameter.

http_only: bool | None

The HttpOnly parameter.

same_site: str | None

The SameSite parameter.

class werkzeug.test.EnvironBuilder(path='/', base_url=None, query_string=None, method='GET', input_stream=None, content_type=None, content_length=None, errors_stream=None, multithread=False, multiprocess=False, run_once=False, headers=None, data=None, environ_base=None, environ_overrides=None, mimetype=None, json=None, auth=None)

This class can be used to conveniently create a WSGI environment for testing purposes. It can be used to quickly create WSGI environments or request objects from arbitrary data.

The signature of this class is also used in some other places as of Werkzeug 0.5 (create_environ(), Response.from_values(), Client.open()). Because of this most of the functionality is available through the constructor alone.

Files and regular form data can be manipulated independently of each other with the form and files attributes, but are passed with the same argument to the constructor: data.

data can be any of these values:

  • a str or bytes object: The object is converted into an input_stream, the content_length is set and you have to provide a content_type.

  • a dict or MultiDict: The keys have to be strings. The values have to be either any of the following objects, or a list of any of the following objects:

    • a file-like object: These are converted into FileStorage objects automatically.

    • a tuple: The add_file() method is called with the key and the unpacked tuple items as positional arguments.

    • a str: The string is set as form data for the associated key.

  • a file-like object: The object content is loaded in memory and then handled like a regular str or a bytes.

  • path (str) – the path of the request. In the WSGI environment this will end up as PATH_INFO. If the query_string is not defined and there is a question mark in the path everything after it is used as query string.

  • base_url (str | None) – the base URL is a URL that is used to extract the WSGI URL scheme, host (server name + server port) and the script root (SCRIPT_NAME).

  • query_string (t.Mapping[str, str] | str | None) – an optional string or dict with URL parameters.

  • method (str) – the HTTP method to use, defaults to GET.

  • input_stream (t.IO[bytes] | None) – an optional input stream. Do not specify this and data. As soon as an input stream is set you can’t modify args and files unless you set the input_stream to None again.

  • content_type (str | None) – The content type for the request. As of 0.5 you don’t have to provide this when specifying files and form data via data.

  • content_length (int | None) – The content length for the request. You don’t have to specify this when providing data via data.

  • errors_stream (t.IO[str] | None) – an optional error stream that is used for wsgi.errors. Defaults to stderr.

  • multithread (bool) – controls wsgi.multithread. Defaults to False.

  • multiprocess (bool) – controls wsgi.multiprocess. Defaults to False.

  • run_once (bool) – controls wsgi.run_once. Defaults to False.

  • headers (Headers | t.Iterable[tuple[str, str]] | None) – an optional list or Headers object of headers.

  • data (None | (t.IO[bytes] | str | bytes | t.Mapping[str, t.Any])) – a string or dict of form data or a file-object. See explanation above.

  • json (t.Mapping[str, t.Any] | None) – An object to be serialized and assigned to data. Defaults the content type to "application/json". Serialized with the function assigned to json_dumps.

  • environ_base (t.Mapping[str, t.Any] | None) – an optional dict of environment defaults.

  • environ_overrides (t.Mapping[str, t.Any] | None) – an optional dict of environment overrides.

  • auth (Authorization | tuple[str, str] | None) – An authorization object to use for the Authorization header value. A (username, password) tuple is a shortcut for Basic authorization.

  • mimetype (str | None)

Changed in version 3.0: The charset parameter was removed.


Changed in version 2.1: CONTENT_TYPE and CONTENT_LENGTH are not duplicated as header keys in the environ.

Changed in version 2.0: REQUEST_URI and RAW_URI is the full raw URI including the query string, not only the path.

Changed in version 2.0: The default request_class is Request instead of BaseRequest.

Added in version 2.0: Added the auth parameter.

Added in version 0.15: The json param and json_dumps() method.

Added in version 0.15: The environ has keys REQUEST_URI and RAW_URI containing the path before percent-decoding. This is not part of the WSGI PEP, but many WSGI servers include it.

Changed in version 0.6: path and base_url can now be unicode strings that are encoded with iri_to_uri().

server_protocol = 'HTTP/1.1'

the server protocol to use. defaults to HTTP/1.1

wsgi_version = (1, 0)

the wsgi version to use. defaults to (1, 0)


The default request class used by get_request().

alias of Request

static json_dumps(obj, *, skipkeys=False, ensure_ascii=True, check_circular=True, allow_nan=True, cls=None, indent=None, separators=None, default=None, sort_keys=False, **kw)

The serialization function used when json is passed.

classmethod from_environ(environ, **kwargs)

Turn an environ dict back into a builder. Any extra kwargs override the args extracted from the environ.


Changed in version 2.0: Path and query values are passed through the WSGI decoding dance to avoid double encoding.

Added in version 0.15.

  • environ (WSGIEnvironment)

  • kwargs (t.Any)

Return type:


property base_url: str

The base URL is used to extract the URL scheme, host name, port, and root path.

property content_type: str | None

The content type for the request. Reflected from and to the headers. Do not set if you set files or form for auto detection.

property mimetype: str | None

The mimetype (content type without charset etc.)


Added in version 0.14.

property mimetype_params: Mapping[str, str]

The mimetype parameters as dict. For example if the content type is text/html; charset=utf-8 the params would be {'charset': 'utf-8'}.


Added in version 0.14.

property content_length: int | None

The content length as integer. Reflected from and to the headers. Do not set if you set files or form for auto detection.

property form: MultiDict[str, str]

A MultiDict of form values.

property files: FileMultiDict

A FileMultiDict of uploaded files. Use add_file() to add new files.

property input_stream: IO[bytes] | None

An optional input stream. This is mutually exclusive with setting form and files, setting it will clear those. Do not provide this if the method is not POST or another method that has a body.

property query_string: str

The query string. If you set this to a string args will no longer be available.

property args: MultiDict[str, str]

The URL arguments as MultiDict.

property server_name: str

The server name (read-only, use host to set)

property server_port: int

The server port as integer (read-only, use host to set)


Closes all files. If you put real file objects into the files dict you can call this method to automatically close them all in one go.

Return type:



Return the built environ.


Changed in version 0.15: The content type and length headers are set based on input stream detection. Previously this only set the WSGI keys.

Return type:



Returns a request with the data. If the request class is not specified request_class is used.


cls (type[Request] | None) – The request wrapper to use.

Return type:


werkzeug.test.create_environ(*args, **kwargs)

Create a new WSGI environ dict based on the values passed. The first parameter should be the path of the request which defaults to ‘/’. The second one can either be an absolute path (in that case the host is localhost:80) or a full path to the request with scheme, netloc port and the path to the script.

This accepts the same arguments as the EnvironBuilder constructor.


Changed in version 0.5: This function is now a thin wrapper over EnvironBuilder which was added in 0.5. The headers, environ_base, environ_overrides and charset parameters were added.

  • args (t.Any)

  • kwargs (t.Any)

Return type:


werkzeug.test.run_wsgi_app(app, environ, buffered=False)

Return a tuple in the form (app_iter, status, headers) of the application output. This works best if you pass it an application that returns an iterator all the time.

Sometimes applications may use the write() callable returned by the start_response function. This tries to resolve such edge cases automatically. But if you don’t get the expected output you should set buffered to True which enforces buffering.

If passed an invalid WSGI application the behavior of this function is undefined. Never pass non-conforming WSGI applications to this function.

  • app (WSGIApplication) – the application to execute.

  • buffered (bool) – set to True to enforce buffering.

  • environ (WSGIEnvironment)


tuple in the form (app_iter, status, headers)

Return type:

tuple[t.Iterable[bytes], str, Headers]