Unit testing

It is a good practice to separate core business logic from handler, and more generally, interceptor code. This separation of concerns has many benefits, including facilitating testing at the interceptor, interceptor chain and end-to-end response generation levels.

Testing interceptors in isolation

Interceptors can be tested in isolation by either directly invoking the :enter, :leave or :error functions with a mock context map in your test or by using the interceptor chain execute function. Both approaches are demonstrated below.

Given the following interceptor:

(def widget-finder
      {:enter (fn [ctx]
                (assoc ctx :widget {:id 1 :title "foobar"} ))}))

We can test it either directly:

(let [test-fn (:enter widget-finder)]
  (is (= {:id 1 :title "foobar"} (:widget (test-fn {})))))

Or using the interceptor chain execute function:

(is (= {:id 1 :title "foobar"} (:widget (chain/execute {} [widget-finder]))))

We can extend this approach to test coordination across multiple interceptors as follows:

(def widget-renderer
   {:leave (fn [ctx]
             (if-let [widget (:widget ctx)]
               (assoc ctx :response {:status 200
                                     :body   (format "Widget ID %d, Title '%s'"
                                                     (:id widget)
                                                     (:title widget))})
               (assoc ctx :response {:status 404 :body "Not Found"})))}))

(is (= "Widget ID 1, Title 'foobar'"
       (get-in (chain/execute {} [widget-renderer widget-finder])
               [:response :body])))

Testing your service with response-for

The value in exercising the end-to-end operation of your service endpoints is that it provides quick feedback that you’ve wired things up correctly. Pedestal provides the test helper response-for utility function to facilitate testing of services without having to spin up an http server.

This style of testing ensures that routing is correct, and it fully exercises routing, interceptors, and any business logic.

The response-for helper function is specific to servlet-based services and simulates the receipt of a servlet request and creation of a servlet response - but does so without the overhead of an actual HTTP connection, which ensures your tests are fast.

`response-for takes as arguments a service function, verb and url as required parameters; headers and a request body are optional. Let us examine those parameters in more detail.

The service function refers to the :io.pedestal.http/service-fn key value in the service map during service initialization.

The verb is an HTTP method represented as a keyword (i.e., :get, :post, :delete, etc…​).

The url is a relative url represented as a string.

The headers and request body inputs are optional and specified with the :headers and :body keys, respectively.


Before using response-for in tests, a test service must be created. This is done by calling io.pedestal.http/create-servlet with the service map as a parameter. The resulting service-fn can be bound to a var and used in subsequent tests.

(def service (:io.pedestal.http/service-fn (io.pedestal.http/create-servlet service-map)))

Testing GET

The following example illustrates a simple execution of response-for within a test:

(is (= "Hello!" (:body (response-for service :get "/hello"))))

The response returned by response-for contains :status, :body and :header keys. The value of the :headers key is a map with stringified keys. Testing header values would look something like this:

(is (= "text/plain"
       (get-in (response-for service :get "/hello") [:headers "Content-Type"])))

Testing POST

POST’ing to a service endpoint can be tested by using the :post verb and specifying a request :body. The route under test typically includes the body-params interceptor to support request payload parsing. Therefore, you will need to set the Content-Type header of the test request to the appropriate value based on the payload format of the request body.

(is (= 200 (:status (response-for service
                                  :post "/foo"
                                  :headers {"Content-Type" "application/json"}
                                  :body "{\"foo\":\"bar\"}"))))
(is (= 200 (:status (response-for service
                                  :post "/foo-login"
                                  :headers {"Content-Type" "application/x-www-form-urlencoded"}
                                  :body "username=test@test.com&password=my-pwd"))))

Notice how Content-Type is a string.

Constructing route URLs

Pedestal provides a utility, url-for-routes. This is passed the expanded routes for your application, and returns a function that will generate a URL for a specific route; primarily by specifying the route name, but also other factors.

It is recommended to create a url-for test helper based on url-for-routes, and use that helper to create the relative urls for your tests. This allows you to refer to routes by name as opposed to hard-coded paths. Route names are typically more stable. Aside from that, it makes it easy to test routes which use query or path parameters.

Here’s an example:

(require '[io.pedestal.http.route :as http.routes])

(def routes #{["/user/:id/items" :post `user-items]} ; (1)

(def url-for (http.routes/url-for-routes (http.routes/expand-routes routes))))

(is (= 200 (:status (response-for service
                                  :get (url-for ::user-items ;(2)
                                                 :path-params {:id 1}
                                                 :query-params {:sort "ASC"})))))
1 The namespace qualified symbol for user-items will be the default route name (as a keyword)
2 The route name is used to get the URL back

Testing Async interactions

Nothing special needs to be done when testing routes which include async interactions. The response-for helper forces asynchronous request processing to synchronous processing for test purposes.