Unit Tests


The %base desk includes a -test thread which can run unit tests you've written. A test is a Hoon file which produces a core. The -test thread will look for any arms in the core whose name begin with test-, e.g:

++ test-foo
++ test-bar
++ test-foo-bar

Any arms that don't begin with test- will be ignored. Each test- arm must produce a tang (a (list tank)). If the tang is empty (~), it indicates success. If the tang is non-empty, it indicates failure, and the contents of the tang is the error message.

To make test-writing easier, the %base desk includes the /lib/test.hoon library which you can import into your test file. The library contains four functions which all produce tangs:

  • expect-eq - test whether an expression produces the expected value. This function takes [expected=vase actual=vase], comparing .expected to .actual.
  • expect - test whether an expression produces %.y. This function takes a vase containing the result to check.
  • expect-fail - tests whether the given trap crashes, failing if it succeeds.
  • category - this is a utility that prepends an error message to a failed test (non-null tang), passing through an empty tang (successful test) unchanged.

The most commonly used function is expect-eq, which is used like:

++ test-foo
%+ expect-eq
!> 'the result I expect'
!> (function-i-want-to-test 'some argument')

Of course, you'll want to test something else you've written rather than just expressions in the test file itself. To do that, you'd just import the file with /= or a similar Ford rune, and then call its functions in the test arms. You're free to do any compositions, import types, etc, as long as the file ultimately produces a core with test-* arms.


The -test thread takes a (list path) in the Dojo, where each path is a path to a test file. The path must include the full path prefix (/[ship]/[desk]/[case]). The path may omit the mark, since a .hoon file is assumed. The path may include the name of a test arm after the filename. In that case, only the specified test arm will be run.

The conventional location for tests is a /tests directory in the root of a desk.

The output of the -test thread will note which arms were tested and whether they succeeded. It will also include:

  • The number of micro-seconds it took to execute each test arm.
  • A ? specifying whether all tests succeeded.
  • A message confirming the file was built successfully.

Here's an example of running the tests for the naive.hoon library:

> -test %/tests/lib/naive ~
built /tests/lib/naive/hoon
> test-zod-spawn-to-zero: took 81359µs
OK /lib/naive/test-zod-spawn-to-zero
> test-zod-spawn-proxy: took 128125µs
OK /lib/naive/test-zod-spawn-proxy
....truncated for brevity....
> test-approval-for-all: took 647403µs
OK /lib/naive/test-approval-for-all
> test-address-padding: took 75104µs
OK /lib/naive/test-address-padding

Here's an example of running just a single test for naive.hoon, the ++test-deposit arm:

> -test %/tests/lib/naive/test-deposit ~
built /tests/lib/naive/hoon
> test-deposit: took ms/45.542
OK /lib/naive/test-deposit

More info

A good reference example is the test file for the /lib/number-to-words.hoon library, located in /tests/lib/number-to-words.hoon. Note that the /tests directory is not typically included in standard pills. If you want to have a look at existing tests as a reference, you may need to clone the urbit/urbit repo on Github.

If you write tests for some of your code, you may wish to exclude the /tests directory from the production version of your desk.