fix: improve get_db_engine_spec_for_backend (#21171)

* fix: improve get_db_engine_spec_for_backend

* Fix tests

* Fix docs

* fix lint

* fix fallback

* Fix engine validation

* Fix test

tests/unit_tests/databases/schema_tests.py

@@ -0,0 +1,193 @@
+# 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.
+
+# pylint: disable=import-outside-toplevel, invalid-name, unused-argument, redefined-outer-name
+
+from typing import TYPE_CHECKING
+
+import pytest
+from marshmallow import fields, Schema, ValidationError
+from pytest_mock import MockFixture
+
+if TYPE_CHECKING:
+    from superset.databases.schemas import DatabaseParametersSchemaMixin
+    from superset.db_engine_specs.base import BasicParametersMixin
+
+
+# pylint: disable=too-few-public-methods
+class InvalidEngine:
+    """
+    An invalid DB engine spec.
+    """
+
+
+@pytest.fixture
+def dummy_schema() -> "DatabaseParametersSchemaMixin":
+    """
+    Fixture providing a dummy schema.
+    """
+    from superset.databases.schemas import DatabaseParametersSchemaMixin
+
+    class DummySchema(Schema, DatabaseParametersSchemaMixin):
+        sqlalchemy_uri = fields.String()
+
+    return DummySchema()
+
+
+@pytest.fixture
+def dummy_engine(mocker: MockFixture) -> None:
+    """
+    Fixture proving a dummy DB engine spec.
+    """
+    from superset.db_engine_specs.base import BasicParametersMixin
+
+    class DummyEngine(BasicParametersMixin):
+        engine = "dummy"
+        default_driver = "dummy"
+
+    mocker.patch("superset.databases.schemas.get_engine_spec", return_value=DummyEngine)
+
+
+def test_database_parameters_schema_mixin(
+    dummy_engine: None,
+    dummy_schema: "Schema",
+) -> None:
+    from superset.models.core import ConfigurationMethod
+
+    payload = {
+        "engine": "dummy_engine",
+        "configuration_method": ConfigurationMethod.DYNAMIC_FORM,
+        "parameters": {
+            "username": "username",
+            "password": "password",
+            "host": "localhost",
+            "port": 12345,
+            "database": "dbname",
+        },
+    }
+    result = dummy_schema.load(payload)
+    assert result == {
+        "configuration_method": ConfigurationMethod.DYNAMIC_FORM,
+        "sqlalchemy_uri": "dummy+dummy://username:password@localhost:12345/dbname",
+    }
+
+
+def test_database_parameters_schema_mixin_no_engine(
+    dummy_schema: "Schema",
+) -> None:
+    from superset.models.core import ConfigurationMethod
+
+    payload = {
+        "configuration_method": ConfigurationMethod.DYNAMIC_FORM,
+        "parameters": {
+            "username": "username",
+            "password": "password",
+            "host": "localhost",
+            "port": 12345,
+            "database": "dbname",
+        },
+    }
+    try:
+        dummy_schema.load(payload)
+    except ValidationError as err:
+        assert err.messages == {
+            "_schema": [
+                (
+                    "An engine must be specified when passing individual parameters to "
+                    "a database."
+                ),
+            ]
+        }
+
+
+def test_database_parameters_schema_mixin_invalid_engine(
+    dummy_engine: None,
+    dummy_schema: "Schema",
+) -> None:
+    from superset.models.core import ConfigurationMethod
+
+    payload = {
+        "engine": "dummy_engine",
+        "configuration_method": ConfigurationMethod.DYNAMIC_FORM,
+        "parameters": {
+            "username": "username",
+            "password": "password",
+            "host": "localhost",
+            "port": 12345,
+            "database": "dbname",
+        },
+    }
+    try:
+        dummy_schema.load(payload)
+    except ValidationError as err:
+        print(err.messages)
+        assert err.messages == {
+            "_schema": ['Engine "dummy_engine" is not a valid engine.']
+        }
+
+
+def test_database_parameters_schema_no_mixin(
+    dummy_engine: None,
+    dummy_schema: "Schema",
+) -> None:
+    from superset.models.core import ConfigurationMethod
+
+    payload = {
+        "engine": "invalid_engine",
+        "configuration_method": ConfigurationMethod.DYNAMIC_FORM,
+        "parameters": {
+            "username": "username",
+            "password": "password",
+            "host": "localhost",
+            "port": 12345,
+            "database": "dbname",
+        },
+    }
+    try:
+        dummy_schema.load(payload)
+    except ValidationError as err:
+        assert err.messages == {
+            "_schema": [
+                (
+                    'Engine spec "InvalidEngine" does not support '
+                    "being configured via individual parameters."
+                )
+            ]
+        }
+
+
+def test_database_parameters_schema_mixin_invalid_type(
+    dummy_engine: None,
+    dummy_schema: "Schema",
+) -> None:
+    from superset.models.core import ConfigurationMethod
+
+    payload = {
+        "engine": "dummy_engine",
+        "configuration_method": ConfigurationMethod.DYNAMIC_FORM,
+        "parameters": {
+            "username": "username",
+            "password": "password",
+            "host": "localhost",
+            "port": "badport",
+            "database": "dbname",
+        },
+    }
+    try:
+        dummy_schema.load(payload)
+    except ValidationError as err:
+        assert err.messages == {"port": ["Not a valid integer."]}