Ppx_expect is a framework for writing tests in OCaml, similar to Cram
(https://bitheap.org/cram/). Ppx_expect mimics 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.