feat: add endpoint to fetch available DBs (#14208)

* feat: add endpoint to fetch available DBs

* Fix lint

tests/databases/schema_tests.py

@@ -0,0 +1,125 @@
+# 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 marshmallow import fields, Schema, ValidationError
+
+from superset.databases.schemas import DatabaseParametersSchemaMixin
+from superset.db_engine_specs.base import BaseParametersMixin
+
+
+class DummySchema(Schema, DatabaseParametersSchemaMixin):
+    sqlalchemy_uri = fields.String()
+
+
+class DummyEngine(BaseParametersMixin):
+    drivername = "dummy"
+
+
+class InvalidEngine:
+    pass
+
+
+@mock.patch("superset.databases.schemas.get_engine_specs")
+def test_database_parameters_schema_mixin(get_engine_specs):
+    get_engine_specs.return_value = {"dummy_engine": DummyEngine}
+    payload = {
+        "parameters": {
+            "engine": "dummy_engine",
+            "username": "username",
+            "password": "password",
+            "host": "localhost",
+            "port": 12345,
+            "database": "dbname",
+        }
+    }
+    schema = DummySchema()
+    result = schema.load(payload)
+    assert result == {
+        "sqlalchemy_uri": "dummy://username:password@localhost:12345/dbname"
+    }
+
+
+def test_database_parameters_schema_mixin_no_engine():
+    payload = {
+        "parameters": {
+            "username": "username",
+            "password": "password",
+            "host": "localhost",
+            "port": 12345,
+            "dbname": "dbname",
+        }
+    }
+    schema = DummySchema()
+    try:
+        schema.load(payload)
+    except ValidationError as err:
+        assert err.messages == {
+            "_schema": [
+                "An engine must be specified when passing individual parameters to a database."
+            ]
+        }
+
+
+@mock.patch("superset.databases.schemas.get_engine_specs")
+def test_database_parameters_schema_mixin_invalid_engine(get_engine_specs):
+    get_engine_specs.return_value = {}
+    payload = {
+        "parameters": {
+            "engine": "dummy_engine",
+            "username": "username",
+            "password": "password",
+            "host": "localhost",
+            "port": 12345,
+            "dbname": "dbname",
+        }
+    }
+    schema = DummySchema()
+    try:
+        schema.load(payload)
+    except ValidationError as err:
+        assert err.messages == {
+            "_schema": ['Engine "dummy_engine" is not a valid engine.']
+        }
+
+
+@mock.patch("superset.databases.schemas.get_engine_specs")
+def test_database_parameters_schema_no_mixin(get_engine_specs):
+    get_engine_specs.return_value = {"invalid_engine": InvalidEngine}
+    payload = {
+        "parameters": {
+            "engine": "invalid_engine",
+            "username": "username",
+            "password": "password",
+            "host": "localhost",
+            "port": 12345,
+            "database": "dbname",
+        }
+    }
+    schema = DummySchema()
+    try:
+        schema.load(payload)
+    except ValidationError as err:
+        assert err.messages == {
+            "_schema": [
+                (
+                    'Engine spec "InvalidEngine" does not support '
+                    "being configured via individual parameters."
+                )
+            ]
+        }