WIP: Add API tests for metadata handling

tests/metadata/test_metadata_api.py

@@ -0,0 +1,91 @@
+#!/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 pytest
+
+from earthkit.data import from_source
+from earthkit.data.testing import earthkit_examples_file
+
+try:
+    from earthkit.data.metadata import Metadata
+except ImportError:
+    Metadata = None
+
+try:
+    from earthkit.data.metadata import RawMetadata
+except ImportError:
+    RawMetadata = None
+
+try:
+    from earthkit.data.readers.grib.metadata import GribMetadata
+except ImportError:
+    GribMetadata = None
+
+
+def test_abstract_metadata():
+    # Metadata properties:
+    # * immutable
+    # * behaves like a dict
+    # * can be updated (creating a new object, either a copy or a view)
+    # Updates can be made with compatible subclasses, e.g. update a GribMetadata with a RawMetadata
+    assert Metadata is not None
+
+
+def test_raw_metadata():
+    assert RawMetadata is not None
+    assert issubclass(RawMetadata, Metadata)
+
+    md = RawMetadata({"shortName": "2t", "perturbationNumber": 5})
+    assert md["shortName"] == "2t"
+    assert md["perturbationNumber"] == 5
+    assert md.get("shortName") == "2t"
+    with pytest.raises(KeyError):
+        md["nonExistentKey"]
+    assert md.get("nonExistentKey", 12) == 12
+
+    md2 = md.update({"centre": "ecmf", "perturbationNumber": 8})
+    sentinel = object()
+    assert md.get("centre", sentinel) is sentinel
+    assert md["perturbationNumber"] == 5
+    assert md2["shortName"] == "2t"
+    assert md2["perturbationNumber"] == 8
+    assert md2["centre"] == "ecmf"
+
+    md3 = RawMetadata({"step": 24, "centre": "unknown"}).update(md2)
+    assert md3["step"] == 24
+    assert md3["centre"] == "ecmf"
+    assert md3["shortName"] == "2t"
+
+
+def test_grib_metadata():
+    assert GribMetadata is not None
+    assert issubclass(GribMetadata, Metadata)
+
+    with pytest.raises(TypeError):
+        GribMetadata({"shortName": "u", "typeOfLevel": "pl", "levelist": 1000})
+
+    f = from_source("file", earthkit_examples_file("test_single.grib"))
+    md = f[0].metadata()
+
+    assert isinstance(md, GribMetadata)
+
+    assert str(md["dataDate"]) == "20170427"
+    assert md["shortName"] == "2t"
+
+    extra = RawMetadata({"shortName": "2ta"})
+    with pytest.raises(TypeError):
+        extra.update(md)
+
+    updated = md.update(extra)
+    assert md["shortName"] == "2t"
+    assert updated["shortName"] == "2ta"
+    # When we write the GribMetadata, the GRIB keys should be set in the correct
+    # order to produce the expected result