organise python tests in subdirectories

The directories follow the same structure as the modules in
nominatim/.

test/python/tools/test_sp_csv_loader.py

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+"""
+    Tests for methods of the SPCsvLoader class.
+"""
+import pytest
+
+from nominatim.errors import UsageError
+from nominatim.tools.special_phrases.sp_csv_loader import SPCsvLoader
+
+def test_parse_csv(sp_csv_loader):
+    """
+        Test method parse_csv()
+        Should return the right SpecialPhrase objects.
+    """
+    phrases = sp_csv_loader.parse_csv()
+    assert check_phrases_content(phrases)
+
+def test_next(sp_csv_loader):
+    """
+        Test objects returned from the next() method.
+        It should return all SpecialPhrases objects of
+        the sp_csv_test.csv special phrases.
+    """
+    phrases = next(sp_csv_loader)
+    assert check_phrases_content(phrases)
+
+def test_check_csv_validity(sp_csv_loader):
+    """
+        Test method check_csv_validity()
+        It should raise an exception when file with a
+        different exception than .csv is given.
+    """
+    sp_csv_loader.csv_path = 'test.csv'
+    sp_csv_loader.check_csv_validity()
+    sp_csv_loader.csv_path = 'test.wrong'
+    with pytest.raises(UsageError):
+        assert sp_csv_loader.check_csv_validity()
+
+def check_phrases_content(phrases):
+    """
+        Asserts that the given phrases list contains
+        the right phrases of the sp_csv_test.csv special phrases.
+    """
+    return  len(phrases) > 1 \
+            and any(p.p_label == 'Billboard'
+                    and p.p_class == 'advertising'
+                    and p.p_type == 'billboard'
+                    and p.p_operator == '-' for p in phrases) \
+            and any(p.p_label == 'Zip Lines'
+                    and p.p_class == 'aerialway'
+                    and p.p_type == 'zip_line'
+                    and p.p_operator == '-' for p in phrases)
+
+@pytest.fixture
+def sp_csv_loader(src_dir):
+    """
+        Return an instance of SPCsvLoader.
+    """
+    csv_path = (src_dir / 'test' / 'testdata' / 'sp_csv_test.csv').resolve()
+    loader = SPCsvLoader(csv_path)
+    return loader