Add test for pattern

tests/utils/test_patterns.py

@@ -0,0 +1,33 @@
+#!/usr/bin/env python3
+
+# (C) Copyright 2020 ECMWF.
+#
+# This software is licensed under the terms of the Apache Licence Version 2.0
+# which can be obtained at http://www.apache.org/licenses/LICENSE-2.0.
+# In applying this licence, ECMWF does not waive the privileges and immunities
+# granted to it by virtue of its status as an intergovernmental organisation
+# nor does it submit to any jurisdiction.
+#
+
+import datetime
+
+import pytest
+
+from earthkit.data.utils.patterns import Pattern
+
+
+@pytest.mark.parametrize(
+    "pattern,values,expected_value",
+    [
+        ("test.{format}", {"format": ["nc", "grib"]}, ["test.nc", "test.grib"]),
+        ("test_{id}.grib", {"id": [2, 3, "AA"]}, ["test_2.grib", "test_3.grib", "test_AA.grib"]),
+        (
+            "test_{my_date:date(%Y-%m-%d)}_{name}.grib",
+            {"my_date": datetime.datetime(2020, 5, 13), "name": ["t2", "msl"]},
+            ["test_2020-05-13_t2.grib", "test_2020-05-13_msl.grib"],
+        ),
+    ],
+)
+def test_pattern_core(pattern, values, expected_value):
+    p = Pattern(pattern)
+    assert p.substitute(values) == expected_value