Add test cases to ensure default boto session is not used

since the boto session is not thread-safe, using the default session in a multi-threaded scenario will result in concurrency errors

Makefile

@@ -24,8 +24,13 @@ test-quick: .env
 # This rule creates a file named .env that is used by docker-compose for passing
 # the USER_ID and GROUP_ID arguments to the Docker image.
 .env:
+	@touch .env
+ifneq ($(OS),Windows_NT)
+ifneq ($(shell uname -s), Darwin)
 	@echo USER_ID=$(shell id -u) > .env
 	@echo GROUP_ID=$(shell id -g) >> .env
+endif
+endif
 	@time docker-compose build
 
 clean:

plugins/redshift/dbt/adapters/redshift/connections.py

@@ -99,7 +99,8 @@ class RedshiftConnectionManager(PostgresConnectionManager):
         must already exist in the database, or else an error will occur"""
 
         if iam_profile is None:
-            boto_client = boto3.client('redshift')
+            session = boto3.Session()
+            boto_client = session.client("redshift")
         else:
             logger.debug("Connecting to Redshift using 'IAM'" +
                          f"with profile {iam_profile}")

test/unit/test_redshift_adapter.py

@@ -1,6 +1,9 @@
 import unittest
 from unittest import mock
+from unittest.mock import Mock
+
 import agate
+import boto3
 
 import dbt.adapters  # noqa
 import dbt.flags as flags
@@ -129,6 +132,23 @@ class TestRedshiftAdapter(unittest.TestCase):
 
         self.assertTrue("'cluster_id' must be provided" in context.exception.msg)
 
+    def test_default_session_is_not_used_when_iam_used(self):
+        boto3.DEFAULT_SESSION = Mock()
+        self.config.credentials = self.config.credentials.replace(method='iam')
+        self.config.credentials.cluster_id = 'clusterid'
+        with mock.patch('dbt.adapters.redshift.connections.boto3.Session'):
+            RedshiftAdapter.ConnectionManager.get_credentials(self.config.credentials)
+            self.assertEquals(boto3.DEFAULT_SESSION.client.call_count, 0,
+                              "The redshift client should not be created using the default session because the session object is not thread-safe")
+
+    def test_default_session_is_not_used_when_iam_not_used(self):
+        boto3.DEFAULT_SESSION = Mock()
+        self.config.credentials = self.config.credentials.replace(method=None)
+        with mock.patch('dbt.adapters.redshift.connections.boto3.Session'):
+            RedshiftAdapter.ConnectionManager.get_credentials(self.config.credentials)
+            self.assertEquals(boto3.DEFAULT_SESSION.client.call_count, 0,
+                              "The redshift client should not be created using the default session because the session object is not thread-safe")
+
     def test_cancel_open_connections_empty(self):
         self.assertEqual(len(list(self.adapter.cancel_open_connections())), 0)