Support using flag --skipslow instead of -m "not slow" for pytest

.github/workflows/ci.yaml

@@ -130,7 +130,7 @@ jobs:
       - name: Run pytest
         run: |
           echo '::add-matcher::.github/problem-matchers/pytest.json'
-          check/pytest -n auto -m "not slow"
+          check/pytest -n auto --skipslow
 
   pytest-extra:
     name: Extra unit tests
@@ -162,7 +162,7 @@ jobs:
       - name: Run pytest
         run: |
           echo '::add-matcher::.github/problem-matchers/pytest.json'
-          check/pytest -n auto -m "not slow" src/openfermion/resource_estimates
+          check/pytest -n auto --skipslow src/openfermion/resource_estimates
 
   pytest-compat:
     name: Python compatibility tests
@@ -190,7 +190,7 @@ jobs:
       - name: Run pytest
         run: |
           echo '::add-matcher::.github/problem-matchers/pytest.json'
-          check/pytest -n auto -m "not slow"
+          check/pytest -n auto --skipslow
 
   coverage:
     name: Python code coverage tests

CONTRIBUTING.md

@@ -293,7 +293,7 @@ We use [pytest](https://docs.pytest.org) to run our tests and
 in the `check/` subdirectory to run these programs.
 
 *   During development, periodically check that code changes do not break anything. For fast checks,
-    run `check/pytest -m "not slow" -n auto PATH ...`, where `PATH ...` is one or more directories
+    run `check/pytest --skipslow -n auto PATH ...`, where `PATH ...` is one or more directories
     or `_test.py` files to test. (The `-n auto` option makes pytest use parallel processes; omit it
     if it causes problems on your system.)
 

conftest.py

@@ -66,3 +66,12 @@ def set_threadpool_limits():
             yield
     else:
         yield
+
+
+def pytest_addoption(parser: pytest.Parser) -> None:
+    parser.addoption("--skipslow", action="store_true", help="skips slow tests")
+
+
+def pytest_runtest_setup(item: pytest.Item) -> None:
+    if "slow" in item.keywords and item.config.getoption("skipslow"):
+        pytest.skip("skipped because of --skipslow option")

pyproject.toml

@@ -25,7 +25,7 @@ disable_warnings = ["no-sysmon"]
 
 [tool.pytest.ini_options]
 markers = [
-    """slow: marks tests as slow (deselect with '-m "not slow"')""",
+    """slow: marks tests as slow (skip with '--skipslow')""",
 ]
 filterwarnings = [
     "ignore:Skipped assert_qasm_is_consistent_with_unitary because qiskit.*:UserWarning",