package ppx_expect
Cram like framework for OCaml
Install
Dune Dependency
Authors
Maintainers
Sources
ppx_expect-v0.15.0.tar.gz
sha256=06315a45b43da72f96719bcb183c0177b5198beae8c3ddce357e180a32f9ca7b
Description
Part of the Jane Street's PPX rewriters collection.
Published: 21 Mar 2022
README
README.org
#+TITLE: expect-test - a cram like framework for OCaml ** Introduction Expect-test is a framework for writing tests in OCaml, similar to [[https://bitheap.org/cram/][Cram]]. Expect-tests mimic the existing inline tests framework with the =let%expect_test= construct. The body of an expect-test can contain output-generating code, interleaved with =%expect= extension expressions to denote the expected output. When run, these tests will pass iff the output matches what was expected. If a test fails, a corrected file with the suffix ".corrected" will be produced with the actual output, and the =inline_tests_runner= will output a diff. Here is an example Expect-test program, say in =foo.ml= #+begin_src ocaml open Core let%expect_test "addition" = printf "%d" (1 + 2); [%expect {| 4 |}] #+end_src When the test is run (as part of =inline_tests_runner=), =foo.ml.corrected= will be produced with the contents: #+begin_src ocaml open Core let%expect_test "addition" = printf "%d" (1 + 2); [%expect {| 3 |}] #+end_src =inline_tests_runner= will also output the diff: #+begin_src ---foo.ml +++foo.ml.corrected File "foo.ml", line 5, characters 0-1: open Core let%expect_test "addition" = printf "%d" (1 + 2); -| [%expect {| 4 |}] +| [%expect {| 3 |}] #+end_src Diffs will be shown in color if the =-use-color= flag is passed to the test runner executable. ** Expects reached from multiple places A [%expect] can exist in a way that it is encountered multiple times, e.g. in a functor or a function: #+begin_src ocaml let%expect_test _ = let f output = print_string output; [%expect {| hello world |}] in f "hello world"; f "hello world"; ;; #+end_src The =[%expect]= should capture the exact same output (i.e. up to string equality) at every invocation. In particular, this does **not** work: #+begin_src ocaml let%expect_test _ = let f output = print_string output; [%expect {| \(foo\|bar\) (regexp) |}] in f "foo"; f "bar"; ;; #+end_src ** Output matching Matching is done on a line-by-line basis. If any output line fails to match its expected output, the expected line is replaced with the actual line in the final output. *** Whitespace Inside =%expect= nodes, whitespace around patterns are ignored, and the user is free to put any amount for formatting purposes. The same goes for the actual output. Ignoring surrounding whitespace allows to write nicely formatted expectation and focus only on matching the bits that matter. To do this, ppx_expect strips patterns and outputs by taking the smallest rectangle of text that contains the non-whitespace material. All end of line whitespace are ignored as well. So for instance all these lines are equivalent: #+begin_src ocaml print blah; [%expect {| abc defg hij|}] print blah; [%expect {| abc defg hij |}] print blah; [%expect {| abc defg hij |}] #+end_src However, the last one is nicer to read. For the rare cases where one does care about what the exact output is, ppx_expect provides the =%expect_exact= extension point, which only succeed when the untouched output is exactly equal to the untouched pattern. When producing a correction, ppx_expect tries to respect as much as possible the formatting of the pattern. ** Output capture The extension point =[%expect.output]= returns a =string= with the output that would have been matched had an =[%expect]= node been there instead. An idiom for testing non-deterministic output is to capture the output using =[%expect.output]= and either post-process it or inspect it manually, e.g., #+BEGIN_SRC ocaml show_process (); let pid_and_exit_status = [%expect.output] in let exit_status = discard_pid pid_and_exit_status in print_endline exit_status; [%expect {| 1 |}] #+END_SRC This is preferred over output patterns (see below). ** Integration with Async, Lwt or other cooperative libraries If you are writing expect tests for a system using Async, Lwt or any other libraries for cooperative threading, you need some preparation so that everything works well. For instance, you probably need to flush some =stdout= channel. The expect test runtime takes care of flushing =Stdlib.stdout= but it doesn't know about =Async.Writer.stdout=, =Lwt_io.stdout= or anything else. To deal with this, expect\_test provides some hooks in the form of a configuration module =Expect_test_config=. The default module in scope define no-op hooks that the user can override. =Async= redefines this module so when =Async= is opened you can write async-aware expect test. In addition to =Async.Expect_test_config=, there is an alternative, =Async.Expect_test_config_with_unit_expect=. That is easier to use than =Async.Expect_test_config= because =[%expect]= has type =unit= rather than =unit Deferred.t=. So one can write: #+begin_src ocaml [%expect foo]; #+end_src rather than: #+begin_src ocaml let%bind () = [%expect foo] in #+end_src =Expect_test_config_with_unit_expect= arrived in 2019-06. We hope to transition from =Expect_test_config= to =Expect_test_config_with_unit_expect=, eventually renaming the latter as the former. *** LWT This is what you would need to write expect tests with Lwt: #+begin_src ocaml module Lwt_io_run = struct type 'a t = 'a Lwt.t end module Lwt_io_flush = struct type 'a t = 'a Lwt.t let return x = Lwt.return x let bind x ~f = Lwt.bind x f let to_run x = x end module Expect_test_config : Expect_test_config_types.S with module IO_run = Lwt_io_run and module IO_flush = Lwt_io_flush = struct module IO_run = Lwt_io_run module IO_flush = Lwt_io_flush let run x = Lwt_main.run (x ()) let flushed () = Lwt_io.(buffered stdout = 0) let upon_unreleasable_issue = `CR end #+end_src ** Comparing Expect-test and unit testing (e.g. =let%test_unit=) The simple example above can be easily represented as a unit test: #+begin_src ocaml let%test_unit "addition" = [%test_result: int] (1 + 2) ~expect:4 #+end_src So, why would one use Expect-test rather than a unit test? There are several differences between the two approaches. With a unit test, one must write code that explicitly checks that the actual behavior agrees with the expected behavior. =%test_result= is often a convenient way of doing that, but even using that requires: - creating a value to compare - writing the type of that value - having a comparison function on the value - writing down the expected value With Expect-test, we can simply add print statements whose output gives insight into the behavior of the program, and blank =%expect= attributes to collect the output. We then run the program to see if the output is acceptable, and if so, *replace* the original program with its output. E.g we might first write our program like this: #+begin_src ocaml let%expect_test _ = printf "%d" (1 + 2); [%expect {||}] #+end_src The corrected file would contain: #+begin_src ocaml let%expect_test _ = printf "%d" (1 + 2); [%expect {| 3 |}] #+end_src With Expect-test, we only have to write code that prints things that we care about. We don't have to construct expected values or write code to compare them. We get comparison for free by using diff on the output. And a good diff (e.g. patdiff) can make understanding differences between large outputs substantially easier, much easier than typical unit-testing code that simply states that two values aren't equal. Once an Expect-test program produces the desired expected output and we have replaced the original program with its output, we now automatically have a regression test going forward. Any undesired change to the output will lead to a mismatch between the source program and its output. With Expect-test, the source program and its output are interleaved. This makes debugging easier, because we do not have to jump between source and its output and try to line them up. Furthermore, when there is a mismatch, we can simply add print statements to the source program and run it again. This gives us interleaved source and output with the debug messages interleaved in the right place. We might even insert additional empty =%%expect= attributes to collect debug messages. ** Implementation Every =%expect= node in an Expect-test program becomes a point at which the program output is captured. Once the program terminates, the captured outputs are matched against the expected outputs, and interleaved with the original source code to produce the corrected file. Trailing output is appended in a new =%expect= node. ** Build system integration Follow the same rules as for [[https://github.com/janestreet/ppx_inline_test][ppx_inline_test]]. Just make sure to include =ppx_expect.evaluator= as a dependency of the test runner. The [[https://github.com/janestreet/jane-street-tests][Jane Street tests]] contains a few working examples using oasis. ** Output patterns Lines in an =%expect= can end with a "tag" indicating the kind of match to perform. This functionality is deprecated because it interferes with the smooth expect-test workflow of accepting output. One should instead use output post-processing. To enable support for output patterns, your =jbuild= file should have: =((inline_tests ((flags (-allow-output-patterns)))))= Here are the different kinds of output patterns. The =(regexp)= tag will perform regexp matching on the given line: #+begin_src ocaml printf "foo"; [%expect {| foo\|bar (regexp) |}] #+end_src Similarly, the =(glob)= tag will perform glob matching on the given line: #+begin_src ocaml printf "foobarbaz"; [%expect {| {foo,hello}* (glob) |}] #+end_src The =(literal)= tag will force a literal match on a line, and can be useful in edge cases: #+begin_src ocaml printf "foo*bar (regexp)"; [%expect {| foo*bar (regexp) (literal) |}] #+end_src The =(escaped)= tag will treat the line as an escaped literal string, which can be useful for matching unprintable characters. It doesn't support escaped newlines right now.
Dependencies (8)
Dev Dependencies
None
-
ansi-parse
>= "0.4.0"
- arrayjit
- autofonce
- autofonce_config
- autofonce_core
- autofonce_lib
- autofonce_m4
- autofonce_misc
- autofonce_patch
- autofonce_share
-
bio_io
>= "0.2.1" & < "0.7.0"
- bitpack_serializer
- bitwuzla
- bitwuzla-c
- bitwuzla-cxx
-
camelot
>= "1.3.0"
- charInfo_width
- combinaml
-
combinat
< "3.0"
- ctypes_stubs_js
- cudajit
- dap
-
data-encoding
>= "0.6"
- dkml-install-runner
- dream
- dream-pure
- drom
- drom_lib
- drom_toml
- dune-action-plugin
-
electrod
>= "0.1.6" & < "0.2.1"
-
ez_cmdliner
>= "0.2.0"
-
ez_config
>= "0.2.0"
-
ez_file
>= "0.2.0"
-
ez_hash
< "0.5.3"
- ez_opam_file
- ez_search
- ez_subst
-
feather
>= "0.2.0"
-
fiat-p256
< "0.2.0"
-
fiber
>= "3.7.0"
- fiber-lwt
-
GT
>= "0.4.0" & < "0.5.0"
- gccjit
- graphv
- graphv_core
- graphv_core_lib
- graphv_font
- graphv_font_js
- graphv_font_stb_truetype
- graphv_gles2
- graphv_gles2_native
- graphv_gles2_native_impl
- graphv_webgl
- graphv_webgl_impl
- header-check
- hl_yaml
- http
-
http-cookie
>= "4.0.0"
-
http-multipart-formdata
>= "2.0.0"
- hyper
- imguiml
-
influxdb
>= "0.2.0"
-
js_of_ocaml
>= "3.10.0"
-
js_of_ocaml-compiler
>= "3.4.0"
-
js_of_ocaml-lwt
>= "3.10.0"
-
js_of_ocaml-ocamlbuild
>= "3.10.0" & < "5.0"
-
js_of_ocaml-ppx
>= "3.10.0"
-
js_of_ocaml-ppx_deriving_json
>= "3.10.0"
-
js_of_ocaml-toplevel
>= "3.10.0"
-
js_of_ocaml-tyxml
>= "3.10.0"
- kdl
- knights_tour
-
kqueue
>= "0.2.0"
-
learn-ocaml
>= "0.16.0"
-
learn-ocaml-client
>= "0.16.0"
- libbpf
-
little_logger
< "0.3.0"
-
loga
>= "0.0.5"
-
lsp
< "1.8.0" | >= "1.11.3" & < "1.19.0"
- m_tree
-
merge-fmt
>= "0.3"
-
mlt_parser
= "v0.15.0"
- module-graph
- neural_nets_lib
- nloge
-
nsq
>= "0.4.0" & < "0.5.2"
-
OCanren-ppx
>= "0.3.0~alpha1"
-
ocaml-lsp-server
>= "1.15.0-4.14" & < "1.19.0"
-
ocaml-protoc-plugin
>= "1.0.0"
-
ocluster
>= "0.2"
- ocp-search
-
ocplib_stuff
>= "0.3.0"
- octez-libs
- octez-protocol-009-PsFLoren-libs
- octez-protocol-010-PtGRANAD-libs
- octez-protocol-011-PtHangz2-libs
- octez-protocol-012-Psithaca-libs
- octez-protocol-013-PtJakart-libs
- octez-protocol-014-PtKathma-libs
- octez-protocol-015-PtLimaPt-libs
- octez-protocol-016-PtMumbai-libs
- octez-protocol-017-PtNairob-libs
- octez-protocol-018-Proxford-libs
- octez-protocol-019-PtParisB-libs
- octez-protocol-020-PsParisC-libs
- octez-protocol-alpha-libs
- octez-shell-libs
-
odate
>= "0.6"
-
odoc
>= "2.0.0"
- odoc-parser
-
omd
>= "2.0.0~alpha3"
-
opam-bin
>= "0.9.5"
- opam-check-npm-deps
-
opam_bin_lib
>= "0.9.5"
- owork
- passage
- poll
- pp
-
ppx_jane
= "v0.15.0"
- ppx_minidebug
-
ppx_protocol_conv_json
>= "5.0.0"
-
ppx_relit
>= "0.2.0"
- ppx_ts
-
psmt2-frontend
>= "0.3.0"
- pvec
- pyml_bindgen
-
pythonlib
>= "v0.15.0" & < "v0.16.0"
- res_tailwindcss
-
routes
>= "2.0.0"
-
safemoney
>= "0.1.1"
- sarif
-
sedlex
>= "3.1"
-
seqes
< "0.2"
- solidity-alcotest
- solidity-common
- solidity-parser
- solidity-test
- solidity-typechecker
-
spawn
< "v0.9.0" | >= "v0.14.0"
- tezos-benchmark
-
tezos-client-009-PsFLoren
>= "14.0"
-
tezos-client-010-PtGRANAD
>= "14.0"
-
tezos-client-011-PtHangz2
>= "14.0"
-
tezos-client-012-Psithaca
>= "14.0"
-
tezos-client-013-PtJakart
>= "14.0"
- tezos-client-014-PtKathma
- tezos-client-015-PtLimaPt
- tezos-client-016-PtMumbai
- tezos-client-017-PtNairob
-
tezos-client-alpha
>= "14.0"
- tezos-injector-013-PtJakart
- tezos-injector-014-PtKathma
- tezos-injector-015-PtLimaPt
- tezos-injector-016-PtMumbai
- tezos-injector-alpha
- tezos-layer2-utils-016-PtMumbai
- tezos-layer2-utils-017-PtNairob
-
tezos-micheline
>= "14.0"
-
tezos-shell
>= "15.0"
- tezos-smart-rollup-016-PtMumbai
- tezos-smart-rollup-017-PtNairob
- tezos-smart-rollup-alpha
- tezos-smart-rollup-layer2-016-PtMumbai
- tezos-smart-rollup-layer2-017-PtNairob
-
tezos-stdlib
>= "14.0"
- tezos-tx-rollup-013-PtJakart
- tezos-tx-rollup-014-PtKathma
- tezos-tx-rollup-015-PtLimaPt
- tezos-tx-rollup-alpha
-
toplevel_expect_test
>= "v0.15.0" & < "v0.16.0"
-
torch
< "v0.16.0"
-
travesty
>= "0.3.0" & < "0.6.0" | >= "0.7.0" & < "0.8.0"
- um-abt
-
wtr
>= "2.0.0"
- wtr-ppx
- zanuda
Conflicts
None
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