unikernel/duniverse/ocaml-cstruct/ppx_test/errors/README.md

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+This tests error cases for `ppx_cstruct`.
+
+It only deals with the errors raised by the ppx itself (such as when the type is
+not supported), not errors in the generated code.
+
+To add a test case:
+
+- create a file in this directory named `something.ml` with the error case
+- create an empty file named `something.ml.expected`
+- don't forget to add these files to git
+- run `dune runtest`: it displays a diff on `dune.inc`
+- run `dune promote`: it updates `dune.inc` with the generated test case
+- run `dune runtest`: it runs the test and displays a diff against the empty
+  expected output
+- run `dune promote`: it updates `something.ml.expected`