Rename the files in the test_cases directory; add further clarifications to the README (#8688)

test_cases/README.md

@@ -1,9 +1,9 @@
 ## Regression tests for typeshed
 
-This directory contains regression tests for the stubs found elsewhere in the
-typeshed repo.
+This directory contains code samples that act as a regression test for the
+standard library stubs found elsewhere in the typeshed repo.
 
-**This directory should *only* contain tests for functions and classes which
+**This directory should *only* contain test cases for functions and classes which
 are known to have caused problems in the past, where the stubs are difficult to
 get right.** 100% test coverage for typeshed is neither necessary nor
 desirable, as it would lead to code duplication. Moreover, typeshed has
@@ -11,21 +11,25 @@ multiple other mechanisms for spotting errors in the stubs.
 
 ### The purpose of these tests
 
-Different tests in this directory serve different purposes. For some stubs in
+Different test cases in this directory serve different purposes. For some stubs in
 typeshed, the type annotations are complex enough that it's useful to have
 basic sanity checks that test whether a type checker understands the intent of
 the annotations correctly. Examples of tests like these are
-`stdlib/builtins/test_pow.py` and `stdlib/asyncio/test_gather.py`.
+`stdlib/builtins/check_pow.py` and `stdlib/asyncio/check_gather.py`.
 
-Other tests, such as the tests for `ExitStack` in `stdlib/test_contextlib.py`
-and the tests for `LogRecord` in `stdlib/test_logging.py`, do not relate to
+Other test cases, such as the samples for `ExitStack` in `stdlib/check_contextlib.py`
+and the samples for `LogRecord` in `stdlib/check_logging.py`, do not relate to
 stubs where the annotations are particularly complex, but they *do* relate to
 stubs where decisions have been taken that might be slightly unusual. These
-tests serve a different purpose: to check that type checkers do not emit
+test cases serve a different purpose: to check that type checkers do not emit
 false-positive errors for idiomatic usage of these classes.
 
 ### How the tests work
 
+The code in this directory is not intended to be directly executed. Instead,
+type checkers are run on the code, in order to check whether typing errors are
+emitted at the places where we want them to be.
+
 Some files in this directory simply contain samples of idiomatic Python, which
 should not (if the stubs are correct) cause a type checker to emit any errors.
 
@@ -52,19 +56,20 @@ provides a useful guide.
 ### Naming convention
 
 Use the same top-level name for the module / package you would like to test.
-Use `test_${thing}.py` naming pattern for individual test files.
+Use the `check_${thing}.py` naming pattern for individual test files.
 
-By default, tests go into a test file with the same name as the stub file, prefixed with `test_`.
-For example: `stdlib/test_contextlib.py`.
+By default, test cases go into a file with the same name as the stub file, prefixed with `check_`.
+For example: `stdlib/check_contextlib.py`.
 
 If that file becomes too big, we instead create a directory with files named after individual objects being tested.
-For example: `stdlib/builtins/test_dict.py`.
+For example: `stdlib/builtins/check_dict.py`.
 
 ### Differences to the rest of typeshed
 
 Unlike the rest of typeshed, this directory largely contains `.py` files. This
 is because the purpose of this folder is to test the implications of typeshed
-changes for end users.
+changes for end users, who will mainly be using `.py` files rather than `.pyi`
+files.
 
 Another difference to the rest of typeshed is that the test cases in this
 directory cannot always use modern syntax for type hints.

tests/check_consistent.py

@@ -59,9 +59,9 @@ def check_stubs() -> None:
 
 def check_test_cases() -> None:
     assert_consistent_filetypes(Path("test_cases"), kind=".py", allowed={"README.md"})
-    bad_test_case_filename = 'Files in the `test_cases` directory must have names starting with "test_"; got "{}"'
+    bad_test_case_filename = 'Files in the `test_cases` directory must have names starting with "check_"; got "{}"'
     for file in Path("test_cases").rglob("*.py"):
-        assert file.stem.startswith("test_"), bad_test_case_filename.format(file)
+        assert file.stem.startswith("check_"), bad_test_case_filename.format(file)
 
 
 def check_no_symlinks() -> None: