def test_missing_indicator_feature_names_out():
"""Check that missing indicator return the feature names with a prefix."""
pd = pytest.importorskip("pandas")
missing_values = np.nan
X = pd.DataFrame(
[
[missing_values, missing_values, 1, missing_values],
[4, missing_values, 2, 10],
],
columns=["a", "b", "c", "d"],
)
indicator = MissingIndicator(missing_values=missing_values).fit(X)
feature_names = indicator.get_feature_names_out()
expected_names = ["missingindicator_a", "missingindicator_b", "missingindicator_d"]
assert_array_equal(expected_names, feature_names)
