Add missing snapshots. Fix linting issue.

Author: martinmoldrup

__snapshots__/[test_expect_direct_call][test_expect_direct_call].dataframe.csv

@@ -0,0 +1,3 @@
+,x
+0,1
+1,2

__snapshots__/[test_file][test_function].dataframe.csv

@@ -0,0 +1,3 @@
+,key1,key2
+0,value1,test1
+1,value2,test2

__snapshots__/[test_fixture_expect_dataframe][test_expect_dataframe].dataframe.csv

@@ -0,0 +1,3 @@
+,key
+0,value1
+1,value2

__snapshots__/[test_load_snapshot_from_file_dataframe][test_save_dataframe_snapshot].dataframe.csv

@@ -0,0 +1,4 @@
+,numbers
+0,1
+1,2
+2,3

snappylapy/_plugin.py

@@ -131,7 +131,7 @@ def pytest_configure(config: pytest.Config) -> None:
     """Register the markers used."""
     config.addinivalue_line(
         "markers",
-        "snappylapy(foreach_folder_in=None, output_dir=None, depends=None): Mark the test to use snappylapy plugin functionalities.",
+        "snappylapy(foreach_folder_in=None, output_dir=None, depends=None): Mark the test to use snappylapy plugin functionalities.",  # noqa: E501
     )  # TODO: Add link to documentation