X-Git-Url: https://git.madduck.net/etc/vim.git/blobdiff_plain/0b301f80954a026693c4c22de89267ad8c85f9b6..882d8795c6ff65c02f2657e596391748d1b6b7f5:/docs/contributing/the_basics.md

diff --git a/docs/contributing/the_basics.md b/docs/contributing/the_basics.md
index 40d2332..bc1680e 100644
--- a/docs/contributing/the_basics.md
+++ b/docs/contributing/the_basics.md
@@ -37,6 +37,63 @@ the root of the black repo:
 (.venv)$ tox -e run_self
 ```
 
+### Development
+
+Further examples of invoking the tests
+
+```console
+# Run all of the above mentioned, in parallel
+(.venv)$ tox --parallel=auto
+
+# Run tests on a specific python version
+(.venv)$ tox -e py39
+
+# pass arguments to pytest
+(.venv)$ tox -e py -- --no-cov
+
+# print full tree diff, see documentation below
+(.venv)$ tox -e py -- --print-full-tree
+
+# disable diff printing, see documentation below
+(.venv)$ tox -e py -- --print-tree-diff=False
+```
+
+### Testing
+
+All aspects of the _Black_ style should be tested. Normally, tests should be created as
+files in the `tests/data/cases` directory. These files consist of up to three parts:
+
+- A line that starts with `# flags: ` followed by a set of command-line options. For
+  example, if the line is `# flags: --preview --skip-magic-trailing-comma`, the test
+  case will be run with preview mode on and the magic trailing comma off. The options
+  accepted are mostly a subset of those of _Black_ itself, except for the
+  `--minimum-version=` flag, which should be used when testing a grammar feature that
+  works only in newer versions of Python. This flag ensures that we don't try to
+  validate the AST on older versions and tests that we autodetect the Python version
+  correctly when the feature is used. For the exact flags accepted, see the function
+  `get_flags_parser` in `tests/util.py`. If this line is omitted, the default options
+  are used.
+- A block of Python code used as input for the formatter.
+- The line `# output`, followed by the output of _Black_ when run on the previous block.
+  If this is omitted, the test asserts that _Black_ will leave the input code unchanged.
+
+_Black_ has two pytest command-line options affecting test files in `tests/data/` that
+are split into an input part, and an output part, separated by a line with`# output`.
+These can be passed to `pytest` through `tox`, or directly into pytest if not using
+`tox`.
+
+#### `--print-full-tree`
+
+Upon a failing test, print the full concrete syntax tree (CST) as it is after processing
+the input ("actual"), and the tree that's yielded after parsing the output ("expected").
+Note that a test can fail with different output with the same CST. This used to be the
+default, but now defaults to `False`.
+
+#### `--print-tree-diff`
+
+Upon a failing test, print the diff of the trees as described above. This is the
+default. To turn it off pass `--print-tree-diff=False`.
+
 ### News / Changelog Requirement
 
 `Black` has CI that will check for an entry corresponding to your PR in `CHANGES.md`. If