feat: raise exception if database doesnt exist (#96)

Closes #78

I wanted to write a test to assert the exception gets raised and had a
hard time fitting it into the test framework because by the time I
receive the target in the test methods its already instantiated with the
sample config with the valid database so I cant override it in an
individual test. So I'd need to create a suite and call
get_target_test_class just to run a single test, instead I just ran the
components as a standalone test.

---------

Co-authored-by: Edgar R. M. <edgar@meltano.com>

Author: pnadolny13

target_snowflake/connector.py

@@ -134,7 +134,7 @@ def create_engine(self) -> Engine:
         Returns:
             A new SQLAlchemy Engine.
         """
-        return sqlalchemy.create_engine(
+        engine = sqlalchemy.create_engine(
             self.sqlalchemy_url,
             connect_args={
                 "session_parameters": {
@@ -143,6 +143,12 @@ def create_engine(self) -> Engine:
             },
             echo=False,
         )
+        connection = engine.connect()
+        db_names = [db[1] for db in connection.execute(text("SHOW DATABASES;")).fetchall()]
+        if self.config["database"] not in db_names:
+            raise Exception(f"Database '{self.config['database']}' does not exist or the user/role doesn't have access to it.")
+        return engine
+
 
     def prepare_column(
         self,

tests/test_target_snowflake.py

@@ -89,3 +89,14 @@ class TestTargetSnowflake(BaseSnowflakeTargetTests, StandardTargetTests):  # typ
 
 class TestTargetSnowflakeBatch(BaseSnowflakeTargetTests, BatchTargetTests):  # type: ignore[misc, valid-type]  # noqa: E501
     """Batch Target Tests."""
+
+def test_invalid_database():
+    INVALID_TEST_CONFIG = copy.deepcopy(SAMPLE_CONFIG)
+    INVALID_TEST_CONFIG["database"] = "FOO_BAR_DOESNT_EXIST"
+    runner = TargetTestRunner(
+        TargetSnowflake,
+        config=INVALID_TEST_CONFIG,
+        input_filepath="tests/target_test_streams/existing_table.singer"
+    )
+    with pytest.raises(Exception):
+        runner.sync_all()