me.pmatiello/mockfn

This is a library for mockist test-driven development in Clojure. It is meant to be used alongside a regular testing framework such as clojure.test.

Usage

This library is designed to be compatible with any testing framework. All supported features are described below in the Framework-agnostic usage section. For convenience, special support for clojure.test is also available and described in the Syntactic sugar for clojure.test section.

Framework-agnostic usage

In order to use mockfn, it's enough to require it in a test namespace.

(:require [me.pmatiello.mockfn.plain :as mfn]
          [me.pmatiello.mockfn.matchers :as mfn.m]
          ...)

This will bring mockfn features into scope for the namespace.

Stubbing Function Calls

The providing macro replaces functions with mocks. These mocks return preconfigured values when called with the expected arguments.

(testing "providing"
  (mfn/providing [(one-fn) :result]
    (is (= :result (one-fn)))))

As demonstrated below, a mock (one-fn) can be configured with different return values for different arguments.

(testing "providing - one function, different arguments"
  (mfn/providing [(one-fn :argument-1) :result-1
                  (one-fn :argument-2) :result-2]
    (is (= :result-1 (one-fn :argument-1)))
    (is (= :result-2 (one-fn :argument-2)))))

It's also possible to configure multiple mocks, for multiple functions, at once.

(testing "providing with more than one function"
  (mfn/providing [(one-fn :argument) :result-1
                  (other-fn :argument) :result-2]
    (is (= :result-1 (one-fn :argument)))
    (is (= :result-2 (other-fn :argument))))))

Verifying Interactions

The verifying macro works similarly, but also defines an expectation for the number of times a call should be performed during the test. A test will fail if this expectation is not met.

(testing "verifying"
  (mfn/verifying [(one-fn :argument) :result (mfn.m/exactly 1)]
    (is (= :result (one-fn :argument)))))

Notice that the expected number of calls is defined using a matcher.

Argument Matchers

Mocks can be configured to return a specific value for a range of different arguments through matchers.

(testing "argument matchers"
  (mfn/providing [(one-fn (mfn.m/at-least 10) (mfn.m/at-most 20)) 15]
    (is (= 15 (one-fn 12 18))))))

Mocking private functions

Private functions can be mocked by referring to the Var associated with the symbol of the mocked function.

(testing "providing, private function"
  (mfn/providing [(#'pvt-fn) :result]
    (is (= :result (#'pvt-fn)))))

(testing "verifying, private function"
  (mfn/verifying [(#'pvt-fn :argument) :result (mfn.m/exactly 1)]
    (is (= :result (#'pvt-fn :argument)))))

Returning dynamic values

The invoke function allows mocks to dynamically invoke a function with the received arguments and return the output.

(testing "returns dynamic values"
  (mfn/providing
    [(one-fn (matchers/any)) (mfn/invoke identity)]
    (is (= :x (#'one-fn :x)))
    (is (= :y (#'one-fn :y)))))

The same approach can be used to invoke the original implementation to test whether a function has been invoked as expected without overriding its implementation:

(testing "invokes the original implementation"
  (mfn/verifying
    [(one-fn (matchers/any)) (mfn/invoke one-fn) (matchers/exactly 2)]
    (is (= :x (one-fn :x)))
    (is (= :y (one-fn :y)))))

Throwing exceptions

Mocks can be configured to throw exceptions when invoked using the raise function. This can be used to simulate error scenarios in tests.

(testing "throws an exception"
  (mfn/providing 
    [(one-fn) (mfn/raise (ex-info "error!" {}))]
    (is (thrown-with-msg? ExceptionInfo #"error!" (one-fn)))))

Returning different values at each invocation

The me.pmatiello.mockfn.xtras/return-in-order function allows a mock to return a sequence of values in the order they are called. After the last value, it will continue from the first value in the sequence.

(testing "returns values in order"
  (mfn/providing
    [(one-fn) (xtras/return-in-order [:a :b :c])]
    (is (= [:a :b :c :a :b] (repeatedly 5 one-fn))))

Syntactic sugar for clojure.test

Support for clojure.test is provided in the mockfn.clj-test namespace.

(:require [clojure.test :refer :all]
          [me.pmatiello.mockfn.clj-test :as mfn]
          [me.pmatiello.mockfn.matchers :as mfn.m]
          ...)

The mockfn.clj-test/deftest and mockfn.clj-test/testing macros replace clojure.test/deftest and clojure.test/testing and support a flatter (as in not nested) mocking style using mockfn.clj-test/providing and mockfn.clj-test/verifying:

(mfn/deftest deftest-with-builtin-mocking
  (is (= :one-fn (one-fn)))
  (mfn/providing
    (one-fn) :one-fn)

  (mfn/testing "testing with built-in-mocking"
    (is (= :one-fn (one-fn)))
    (is (= :other-fn (other-fn)))
    (mfn/verifying
      (other-fn) :other-fn (mfn.m/exactly 1))))

Note that to leverage the built-in support for mocking in these macros, it's necessary to use the providing and verifying versions provided in the mockfn.clj-test namespace.

Built-in Matchers

The following matchers are included in mockfn:

Matcher	Description	Usage
Generic
any	Matches any value.	(any)
a	Matches if actual value is an instance of the expected type.	(a type)
exactly	Matches if actual value is equal to the expected value.	(exactly value)
pred	Matches if the actual value satisfies the provided predicate function.	(pred pred-fn)
Presence
some	Matches if the actual value is not nil.	(some)
null	Matches if the actual value is nil.	(null)
empty	Matches if the actual value is empty (collection, string, etc).	(empty)
Boolean
truthy	Matches if the actual value is truthy.	(truthy)
falsy	Matches if the actual value is falsy.	(falsy)
Numeric
at-least	Matches if actual value is greater or equal than the expected value.	(at-least value)
at-most	Matches if actual value is less or equal than the expected value.	(at-most value)
between	Matches if actual value is between the lower and upper bounds.	(between lower upper)
String
starts-with	Matches if actual string starts with the expected prefix.	(starts-with prefix)
ends-with	Matches if actual string ends with the expected suffix.	(ends-with suffix)
includes	Matches if actual string includes the expected substring.	(includes substring)
regex	Matches if the expected regular expression matches the actual string.	(regex expression)
Collection
contains-all	Matches if the actual collection contains all expected values.	(contains values)
contains-any	Matches if the actual collection contains any expected values.	(contains-any values)
Operators
not>	Matches if the actual value does not match the provided matcher.	(not> matcher)
and>	Matches if the actual value matches all provided matchers.	(and> m1 m2 ...)
or>	Matches if the actual value matches any of the provided matchers.	(or> m1 m2 ...)
*>	Matches if the the provided matcher matches all remaining arguments.	(*> matcher)

All matchers above are available in the me.pmatiello.mockfn.matchers namespace.

Quirks and Limitations

While providing and verifying calls can be nested, all required stubs and expectations for a single mock must be defined within the same call. Mocking a function in an inner providing or verifying call will override any definitions made in the outer scope for the tests being run in the inner scope.

(testing "nested mocks"
  (mfn/providing [(one-fn :argument-1) :result-1]
    (mfn/providing [(one-fn :argument-2) :result-2
                    (other-fn :argument-3) :result-3]
      (is (thrown? ExceptionInfo (one-fn :argument-1)))
      (is (= :result-2 (one-fn :argument-2)))
      (is (= :result-3 (other-fn :argument-3))))
    (is (= :result-1 (one-fn :argument-1))))))

Development

Information for developing this library.

Running tests

The following command will execute the unit tests:

% clj -X:test

Building

The following command will build a jar file:

% clj -T:build jar

To clean a previous build, run:

% clj -T:build clean

Releasing

Before releasing, update the library version in the build.clj file and the release date in the changelog.

Make a commit and generate a new tag:

% git commit -a -m "Release: ${VERSION}"
% git tag -a "v${VERSION}" -m "Release: ${VERSION}"
% git push
% git push origin "v${VERSION}" 

Run all tests and build the release artifact:

% clj -X:test
% clj -T:build clean
% clj -T:build jar

To release to clojars, run:

% mvn deploy:deploy-file \
      -Dfile=target/mockfn-${VERSION}.jar \
      -DrepositoryId=clojars \
      -Durl=https://clojars.org/repo \
      -DpomFile=target/classes/META-INF/maven/me.pmatiello/mockfn/pom.xml

Note that this step requires clojars to be configured as a server in the local ~/.m2/settings.xml file.

Contribution Policy

This software is open-source, but closed to contributions.

License

Distributed under the Eclipse Public License either version 2.0 or (at your option) any later version.