It is best to refactor you test to a config file and test. Then the simplest way would be to define several config files, in different folders, with different amount of data.
Alternatively, you an pass a parameter(s) and parse it, as below
tests:
def test_b(params):
...
content of conftest.py :
data = [....]
def pytest_addoption(parser):
parser.addoption("--one", action="store_true", help="run one test")
def pytest_generate_tests(metafunc):
if "params" in metafunc.fixturenames:
if metafunc.config.getoption("one"):
metafunc.parametrize("params", data[:1])
else:
metafunc.parametrize("params", data)
See also
How to pass arguments in pytest by command line