mtest: Allow filtering tests by subproject

You could always specify a list of tests to run by passing the names as
arguments to `meson test`. If there were multiple tests with that name (in the
same project or different subprojects), all of them would be run. Now you can:

1. Run all tests with the specified name from a specific subproject: `meson test subprojname:testname`
1. Run all tests defined in a specific subproject: `meson test subprojectname:`

Also forbid ':' in test names. We already forbid this elsewhere, so
should not be a big deal.

1 files changed, 18 insertions, 0 deletions

diff --git a/docs/markdown/snippets/mtest_test_list_subprojects.md b/docs/markdown/snippets/mtest_test_list_subprojects.md
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+## `meson test` can now filter tests by subproject
+
+You could always specify a list of tests to run by passing the names as
+arguments to `meson test`. If there were multiple tests with that name (in the
+same project or different subprojects), all of them would be run. Now you can:
+
+1. Run all tests with the specified name from a specific subproject: `meson test subprojname:testname`
+1. Run all tests defined in a specific subproject: `meson test subprojectname:`
+
+As before, these can all be specified multiple times and mixed:
+
+```sh
+# Run:
+# * All tests called 'name1' or 'name2' and
+# * All tests called 'name3' in subproject 'bar' and
+# * All tests in subproject 'foo'
+$ meson test name1 name2 bar:name3 foo:
+```