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Lazytest: Generic testing backend for Clojure

by Stuart Sierra,

Copyright (c) Stuart Sierra, 2010. All rights reserved. The use and distribution terms for this software are covered by the Eclipse Public License 1.0 ( which can be found in the file LICENSE.html at the root of this distribution. By using this software in any fashion, you are agreeing to be bound by the terms of this license. You must not remove this notice, or any other, from this software.

One Backend, Many Testing Styles

Lazytest aims to be a generic library that can support many different modes and styles of testing. It defines a few generic representations for executable tests (see "Lazytest Internals", below). Any testing code that can be compiled into these representations can take advantage of Lazytest's running and reporting tools.

Getting Started with Leiningen

Note: These instructions require JDK 6.

Copy the sample project in modules/sample-leiningen-project

Put your app sources in src/ and your test sources in test/

Then run:

lein clean
lein deps
java -cp "src:test:classes:lib/*" src test

And watch your tests run automatically whenever you save a file.

Type CTRL+C to stop.

To run your tests just once and stop, run:

java -cp "src:test:classes:lib/*" lazytest.main src test

Getting Started with Maven

Copy the sample project in modules/sample-maven-project

Put your app sources in src/main/clojure/ and your test sources in src/test/clojure/

Then run:

mvn lazytest:watch

And watch your tests run automatically whenever you save a file.

Type CTRL+C to stop.

To run your tests just once and stop, run:

mvn lazytest:run

Testing with 'deftest'

The lazytest.deftest namespace is a drop-in replacement for the clojure.test library. Each test is a function defined with the deftest macro, making assertions with the is macro:

 (ns examples.readme.deftest
   (:use [lazytest.deftest :only (deftest it thrown? thrown-with-msg?)]))

 (deftest t-addition-with-integers
   ;; arbitrary code may be executed here
   (is (= 4 (+ 2 2)))
   (is (= 7 (+ 3 4))))

Testing with 'describe'

The lazytest.describe namespace mimics the behavior-driven testing style popularized by libraries such as RSpec.

Use the describe macro to create a group of tests. Start the group with a documentation string.

(ns examples.readme.groups
  (:use [lazytest.describe :only (describe it)]))

(describe "This application" ...)

If you put a symbol before (or instead of) the string, the full name of the Var or Class to which that symbol resolves will be prepended to the doc string:

(describe + "with integers" ...)
;; resulting doc string is "#'clojure.core/+ with integers"

Within a describe group, use the it macro to create a single test example. Start your example with a documentation string describing what should happen, followed by an expression to test what you think should be true.

(describe + "with integers"
  (it "computes the sum of 1 and 2"
    (= 3 (+ 1 2)))
  (it "computes the sum of 3 and 4"
    (= 7 (+ 3 4))))

Each it example may only contain one expression, which must return logical true to indicate the test passed or logical false to indicate it failed.

Nested Test Groups

Test groups may be nested inside other groups with the testing macro, which has the same syntax as describe but does not define a top-level Var:

(ns examples.readme.nested
  (:use [lazytest.describe :only (describe it testing)]))

(describe "Addition"
  (testing "of integers"
    (it "computes small sums"
      (= 3 (+ 1 2)))
    (it "computes large sums"
      (= 7000 (+ 3000 4000))))
  (testing "of floats"
    (it "computes small sums"
      (> 0.00001 (Math/abs (- 0.3 (+ 0.1 0.2)))))
    (it "computes large sums"
      (> 0.00001 (Math/abs (- 3000.0 (+ 1000.0 2000.0)))))))

Arbitrary Code in an Example

You can create an example that executes arbitrary code with the do-it macro. Wrap each assertion expression in the lazytest.expect/expect macro.

  (:use [lazytest.describe :only (describe do-it)]
        [lazytest.expect :only (expect)]))

(describe "Arithmetic"
  (do-it "after printing"
    (expect (= 4 (+ 2 2)))
    (println "Hello, World!")
    (expect (= -1 (- 4 5)))))

The expect macro is like assert but carries more information about the failure. It throws an exception if the expression does not evaluate to logical true.

If the code inside the do-it macro runs to completion without throwing an exception, the test example is considered to have passed.

Focusing on Indiviaul Tests and Suites

The describe, testing, it, and do-it macros all take an optional metadata map immediately after the docstring.

Adding :focus true to this map will cause only that test/suite to be run. Removing it will return to the normal behavior (run all tests).

When using deftest, you can put :focus true metadata on the symbol name of your test:

(deftest ^:focus my-test

Generating Random Test Data

The lazytest.random namespace provides functions for generating random input data for your tests.

Lazytest Internals

The smallest unit of testing is a test case, which is a function (see lazytest.test-case/test-case). When the function is called, it may throw an exception to indicate failure. If it does not throw an exception, it is assumed to have passed. The return value of a test case is always ignored. Running a test case may have side effects. The macros lazytest.describe/it and lazytest.describe/do-it create test cases.

Tests cases are organized into suites. A test suite is a function (see lazytest.suite/suite) that returns a test sequence. A test sequence (see lazytest.suite/test-seq) is a sequence, possibly lazy, of test cases and/or test suites. Suites, therefore, may be nested inside other suites, but nothing may be nested inside a test case. The macros lazytest.describe/describe and lazytest.describe/testing create test suites.

A test suite function may NOT have side effects; it is only used to generate test cases and/or other test suites.

A test runnner is responsible for expanding suites (see lazytest.suite/expand-suite) and running test cases (see lazytest.test-case/try-test-case). It may also provide feedback on the success of tests as they run. Two built-in runners are provided, see lazytest.runner.console/run-tests and lazytest.runner.debug/run-tests.

The test runner also returns a sequence of results, which are either suite results (see lazytest.suite/suite-result) or test case results (see lazytest.test-case/test-case-result). That sequence of results is passed to a reporter, which formats results for display to the user. One example reporter is provided, see

Making Emacs Indent Tests Properly

Put the following in .emacs

(eval-after-load 'clojure-mode
     (describe 'defun)
     (testing 'defun)
     (given 'defun)
     (using 'defun)
     (with 'defun)
     (it 'defun)
     (do-it 'defun)))
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