package ppx_expect

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Cram like framework for OCaml


Dune Dependency






  • Change ppx_expect so that when -diff-cmd - is passed, they write the .corrected file but don't diff it or exit with a non-zero exit code.

    This is to make expect tests work with jbuilder. Jbuilder uses a separate build tree, so the current behavior of ppx_expect doesn't work well with jbuilder, especially the in-place behavior.

    What is done instead in jbuilder is that after running the test runner, it checks whether a .corrected file was created. If yes, jbuilder does the diffing itself, and by default also replaces the source file by the correction.'

  • Arrange things so that inline expectation tests work with Dune

  • Regexp and glob matching in the output is now deprecated. This gets in the way of the "promote" workflow. People are instead encouraged to prefilter the output before displaying it.

  • Tell the build system via output metadata when a file contains tests


  • In [%expect] expressions, disallowed backtraces, which can vary across compilation configurations (X_LIBRARY_INLINING, flambda, etc.)

  • Improved ppx_expect to support simultaneous runs of inline_tests_runner on the same file.

  • Added expect-test support for reaching a single [%expect] multiple times, where the test only fails if the output was distinct

  • For expect tests, relaxed the rule for %expects that are reached multiple times. Instead of requiring all outputs to be identical, require only that each output individually match the %expect.

  • In synchronous expect tests, [%expect] now captures stderr in addition to stdout. Previously, there was code that did this for Async expect tests. Now, stderr is captured in all expect tests.

  • Improved expect tests to get the current file when the test runs, rather than when it is registered.



  • Always flush Pervasives.stdout in the ppx_expect runtime.

    We already do this, but it was missing in one place.

  • Made the test framework resilient to user changing the current working directory during the test.

  • Print newlines in "-strings as real newlines, not \n

  • The expect test runtime breaks any executable that wants to work even if cwd doesn't exist, like fe does. Fix that.

    It also brings expect tests in line with what ppx_inline_test does, and removes the diff due to absolute paths I was seeing in the output of ./inline_tests_runner -log in some other features. Concretely, here is what changes:

  • Use the new context-free API

  • Change the check in ppx_expect to be a dynamic check. Instead of checking that expect tests appears only at toplevel, we test that they are run in the library they appear.

    This has several consquence:

    • ppx_expect can use Context_free as well and doesn't require two extra passes

    • expect tests can appear inside let%test_module


  • Add dependency on re.emacs


  • Don't remove trailing semicolons when producing a correction.

  • Corrected %expects with double quoted strings don't have the single space padding.

  • In the ppx_expect runtime, flush stdout before redirecting it This is to avoid capturing leftover of the stdout buffer.

  • Make sure the expect-test runtime doesn't generate %collector_never_triggered, which is not accepted by ppx_expect. Instead generate:


  • Make expect tests pass the user description to the inline test runtime

  • Fix a race condition in the ppx_expect runtime

  • Change ppx_expect be more permissive when matching whitespace in actual output. See ppx/ppx_expect/ for details.

    Changes to the implementation of ppx_expect (including some refactoring):

    • factorized the common bits between the runtime and ppx rewriter into one library expect_test_common

    • factorized different structures representing the same thing using polymorphism

    • communicate data structures between the ppx rewriter and runtime using a generated lifter instead of hand-written lifters

    • splitted the matching and correction writing code: the .corrected is now only created when needed instead of all the time

    • added a concrete syntax tree to represent both the actual output and expectation in non-exact mode. This allow to keep the user formatting as much as possible

    • made various bits more re-usable

  • Change the default style of multi-line expectation to:

    %expect {| abc def |}

    More generally, try to preserve the formatting a bit more when correcting from empty or single to multi-line.

  • Arrange things so that when open Async.Std is opened, %expect ... expressions are of type unit Deferred.t and flush stdout before capturing the output.


Initial release.