Attached patch adds -k/--func-regex and -K/--file-regex options to filter tests by function/file names. It modifies makeSuite() and getTestCaseNames() functions of unittest.loader to add an optional filter argument: callback taking a function name as argument and returning False if the test should be ignored. You can use the new options more than once and their argument are regular expressions (case insensitive).

Examples:

- "./python -m test -k subprocess -K pass_fds" runs only 1 function of 1 file: test_subprocess.test_pass_fds()
- "./python -m test -k os$" runs 1 file: test_os
- "./python -m test -K codecencoding" runs 6 files: test_codecencodings_cn, test_codecencodings_hk, test_codecencodings_iso2022, test_codecencodings_jp, test_codecencodings_kr, test_codecencodings_tw

> Attached patch adds -k/--func-regex and -K/--file-regex options to filter
> tests by function/file names.

We need maybe a third option to filter tests by their class name. And we need 
also maybe the opposite option: exclude tests matching a regex. Another 
proposition: --include and --exclude options using the following format:

<file regex>:<class regex>:<function regex>

Each field is optional, examples:

--include "test_subprocess::leak" ignores test_leak function of 
test_subprocess file
--include "codecencoding::" runs the 6 test_codecencoding* files
--include "test_subprocess:^C:" runs only the tests of the io module (not the 
_pyio module)
- etc.

Problem: --exclude (-x) option is already used.

IMHO it would be better to tweak regrtest so that it understand test_file.TestClass.test_method, possibly supporting wildcards.
E.g.:
  - ./python -m test test_subprocess.POSIXProcessTestCase
  - ./python -m test test_subprocess.POSIXProcessTestCase.test_pass_fds
  - ./python -m test '*codecencoding*'
  - ./python -m test 'test_subprocess.C*'

The -x/--exclude option could be extended to support this notation too and make possible to exclude specific tests classes/methods.
Wildcards are less flexible than regex, but I think they are good enough for our use case and simpler to use.

+1 to what Ezio said, though I'd rather have this than not have the functionality at all :)

How about reusing unittest discovery in regrtest?

> How about reusing unittest discovery in regrtest?

Does this feature support filtering by keyword for file names and function names?

File name, class name, method name unless I misremember.

regrtest_regex-2.patch: minor update, just ensure that the patch applies correctly on the default branch.

See also #12626 for a similar suggestion.

This patch doesn't work if run_unittest() is called with an already constructed test suite or test case (the patch in #12626 does).

Already fixed in #12626.