-- `make check TESTNAME=<path-to-test-file>.rs` - Run a single test file
-- `make check-stage1-rpass TESTNAME=<path-to-test-file>.rs` - Run a single
+- `make check TESTNAME=<substring-of-test-name>` - Run a matching set of tests.
+ - `TESTNAME` should be a substring of the tests to match against e.g. it could
+ be the fully qualified test name, or just a part of it.
+ `TESTNAME=collections::hash::map::test_map::test_capacity_not_less_than_len`
+ or `TESTNAME=test_capacity_not_less_than_len`.
+- `make check-stage1-rpass TESTNAME=<substring-of-test-name>` - Run a single