Move selection before repeat

[CanYing0913]

TL;DR

fix #15 #21 #95

Motivation

pytest-repeat currently implements repetition by adding an indirect parameter in pytest_generate_tests. As a result, pytest creates original item count × repeat count items before collection filtering and other pytest_collection_modifyitems hooks run.

For large suites and high repeat counts, this multiplies collection work even for tests that will later be deselected. In real-world cases, collection can take more than an hour while the selected tests themselves only take a few minutes.

What changed

This PR moves repeat expansion until after collection modification and deselection have completed:

1. Collect the original test items once.
2. Apply -k, -m, and other collection filtering/reordering plugins to the original items.
3. Expand only the remaining items according to --count or @pytest.mark.repeat.
4. Pass the final repeated item list to the runner and pytest-xdist.

The implementation also:

• creates an independent item for each repetition;
• preserves the existing [current-total] node ID suffixes, including parameterized IDs such as [param-1-10];
• preserves function, class, module, and session repeat ordering;
• rebuilds fixture requests and copies per-item mutable state so repetitions do not share runtime state;
• keeps collection totals consistent with the final repeated item list.

pytest-xdist and filtering

The repeated items are created before pytest_collection_finish, so xdist workers report the final unique node IDs to the controller and each repetition can be scheduled independently.

For example:

pytest -n 4 -k important --count=10

collects the original tests, applies -k important, expands each selected test ten times, and then distributes those repeated items across workers.

Because filtering now happens before repeat expansion, -k and -m match the original test IDs and markers. Generated repeat suffixes such as [1-10] are not available as filtering targets. Final reports and xdist scheduling still use the suffixed node IDs.

Performance characteristics

Collection hooks such as pytest_itemcollected now run only for the original items, and ordinary pytest_collection_modifyitems implementations process the unexpanded list. The final runner and xdist item list still contains selected item count × repeat count entries, so execution scheduling and final item storage remain proportional to the number of repetitions.

Tests

Added coverage for:

• repeat expansion after -k deselection;
• collection plugins seeing only original items;
• unique final node IDs and --collect-only totals;
• fixture isolation between repetitions;
• pytest-xdist execution with repeated items.

The existing parameterization, repeat marker, step number, unittest, and repeat-scope tests continue to pass.

Locally verified with:

• pytest 6.2.5, 7.4.4, 8.4.2, and 9.0.2;
• pytest-xdist 3.8.0;
• flake8.