Split up tests/db_engine_test.py (#8449)

* Split up db_engine_specs_test.py into a number of targeted files

* Remove db_engine_specs_test.py

* isort

tests/db_engine_specs/postgres_tests.py

@@ -0,0 +1,72 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+from unittest import mock
+
+from sqlalchemy import column, literal_column
+from sqlalchemy.dialects import postgresql
+
+from superset.db_engine_specs.postgres import PostgresEngineSpec
+from tests.db_engine_specs.base_tests import DbEngineSpecTestCase
+
+
+class PostgresTests(DbEngineSpecTestCase):
+    def test_get_table_names(self):
+        """ Make sure postgres doesn't try to remove schema name from table name
+        ie. when try_remove_schema_from_table_name == False. """
+        inspector = mock.Mock()
+        inspector.get_table_names = mock.Mock(return_value=["schema.table", "table_2"])
+        inspector.get_foreign_table_names = mock.Mock(return_value=["table_3"])
+
+        pg_result_expected = ["schema.table", "table_2", "table_3"]
+        pg_result = PostgresEngineSpec.get_table_names(
+            database=mock.ANY, schema="schema", inspector=inspector
+        )
+        self.assertListEqual(pg_result_expected, pg_result)
+
+    def test_time_exp_literal_no_grain(self):
+        col = literal_column("COALESCE(a, b)")
+        expr = PostgresEngineSpec.get_timestamp_expr(col, None, None)
+        result = str(expr.compile(None, dialect=postgresql.dialect()))
+        self.assertEqual(result, "COALESCE(a, b)")
+
+    def test_time_exp_literal_1y_grain(self):
+        col = literal_column("COALESCE(a, b)")
+        expr = PostgresEngineSpec.get_timestamp_expr(col, None, "P1Y")
+        result = str(expr.compile(None, dialect=postgresql.dialect()))
+        self.assertEqual(result, "DATE_TRUNC('year', COALESCE(a, b))")
+
+    def test_time_ex_lowr_col_no_grain(self):
+        col = column("lower_case")
+        expr = PostgresEngineSpec.get_timestamp_expr(col, None, None)
+        result = str(expr.compile(None, dialect=postgresql.dialect()))
+        self.assertEqual(result, "lower_case")
+
+    def test_time_exp_lowr_col_sec_1y(self):
+        col = column("lower_case")
+        expr = PostgresEngineSpec.get_timestamp_expr(col, "epoch_s", "P1Y")
+        result = str(expr.compile(None, dialect=postgresql.dialect()))
+        self.assertEqual(
+            result,
+            "DATE_TRUNC('year', "
+            "(timestamp 'epoch' + lower_case * interval '1 second'))",
+        )
+
+    def test_time_exp_mixd_case_col_1y(self):
+        col = column("MixedCase")
+        expr = PostgresEngineSpec.get_timestamp_expr(col, None, "P1Y")
+        result = str(expr.compile(None, dialect=postgresql.dialect()))
+        self.assertEqual(result, "DATE_TRUNC('year', \"MixedCase\")")