Merge branch 'niklas_issue005_refac_refactor-and-expand-testing' into 'develop'

Modified the test for the 'value_count' statistic. Now all available sampling...

See merge request !4

tests/pytest.ini

+[pytest]
+markers =
+    slow: marks tests as slow (deselect with '-m "not slow"')

tests/test_interface.py

+import numpy as np
+import pandas as pd
+
+from toarstats.interface import calculate_statistics
+
+
+class TestCalculateStatistics:
+    def test_calculate_statistics_simple_input(self):
+        data = pd.DataFrame(
+            range(10), index=pd.date_range(start="2000", periods=10, freq="H")
+        )
+        result = calculate_statistics("daily", "average_values", data)
+        expected_result = pd.DataFrame(
+            {"mean": 4.5}, index=pd.DatetimeIndex(["2000"], freq="D")
+        )
+        pd.testing.assert_frame_equal(result, expected_result)
+
+    def test_calculate_statistics_different_data_capture(self):
+        data = pd.DataFrame(
+            [1, 2, np.nan, 4, 5, np.nan, 7, np.nan, np.nan, np.nan],
+            index=pd.date_range(start="2000", periods=10, freq="H")
+        )
+        result = calculate_statistics("daily", "average_values", data,
+                                      data_capture=0.75)
+        expected_result = pd.DataFrame(
+            {"mean": np.nan}, index=pd.DatetimeIndex(["2000"], freq="D")
+        )
+        pd.testing.assert_frame_equal(result, expected_result)
+        data = pd.DataFrame(
+            range(24),
+            index=pd.date_range(start="2000", periods=24, freq="H")
+        )
+        result = calculate_statistics("daily", "diurnal_cycle", data)
+        expected_result = pd.DataFrame(
+            {"diurnal_cycle": [float(num) for num in range(24)]},
+            index=pd.date_range(start="2000", periods=24, freq="H")
+        )
+        pd.testing.assert_frame_equal(result, expected_result)