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A Leiningen plugin to run your tests in parallel

By default, parallel-test will search your project for tests flagged ^:parallel with metadata. It will first execute all tests not flagged such, then, in parallel, execute all the tests flagged as such.


Put [com.holychao/parallel-test "0.3.2"] into the :plugins vector of your project.clj.

$ lein parallel-test


The default behavior described above is consequent to default configuration and may be overridden. To override the config, it is important to understand the concepts involved around categories, pools, and sequencing.


Categories are categorizations of tests, classified by metadata on the vars holding those tests. Similar to leiningen's default test framework's test selectors, categories create logical groupings of work. The default categorizations are :parallel and :serial, and are determined solely by the presence of a true value for the :parallel key in a var's metadata. Categorization is done with a function of test metadata; the default function is:

    (fn [meta] (if (:parallel meta) :parallel :serial))


Pools are pools of threads consuming work from categories. The default configuration has two pools; the :serial pool has a single thread, which executes each test in series. The :parallel pool scales its number of threads to the number of cores reported by the JVM. It executes tests in parallel until all tests are exhausted. Pools must correspond one to one with categories, and provide a function returning an integer. This function will be invoked once at test time, and a number of threads corresponding to the integer it returns will be created to consume tests from that pool. The default pooling configuration is:

    {:serial (constantly 1)
     :parallel (fn [] (.availableProcessors (Runtime/getRuntime)))}


Sequencing specifies an ordering of categories. When a category is present in sequencing data, all tests from that category must complete prior to the next category beginning to test. Once all specified categories are exhausted, all of the remaining categories will execute in parallel. The default sequencing configuration is:



Parallel-test requires Clojure 1.5 or greater.

Running tests in parallel means exactly that; parallel-test does not tackle the subjects of isolation or concurrent access for you. If your tests or their fixtures make use of resources such as global vars, databases, tcp ports, or other points of contention you will need to roll your own strategy for concurrent access, or for siloing these resources per test.

parallel-test parallelizes on a per-test basis, not on a per-namespace basis. This means:

  1. If you use test-ns-hook, it will be ignored. Parallel-test must adopt responsibility for executing your tests.
  2. Your :once fixtures may be run more than once. They will be run no more than once per pool per category. Given the semantics of fixtures, they do need to be run in each thread running in each pool.


Source Copyright © 2014 Alex Redington. Portions Copyright © 2009-2014 Phil Hagelberg, Alex Osborne, Dan Larkin, and contributors. Portions Copyright © Rich Hickey.

Distributed under the Eclipse Public License, the same as Clojure uses.

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