feat: add sample for low cost instances (#392)

Author: zoercai

samples/samples/snippets.py

@@ -62,6 +62,34 @@ def create_instance(instance_id):
 # [END spanner_create_instance]
 
 
+# [START spanner_create_instance_with_processing_units]
+def create_instance_with_processing_units(instance_id, processing_units):
+    """Creates an instance."""
+    spanner_client = spanner.Client()
+
+    config_name = "{}/instanceConfigs/regional-us-central1".format(
+        spanner_client.project_name
+    )
+
+    instance = spanner_client.instance(
+        instance_id,
+        configuration_name=config_name,
+        display_name="This is a display name.",
+        processing_units=processing_units,
+    )
+
+    operation = instance.create()
+
+    print("Waiting for operation to complete...")
+    operation.result(120)
+
+    print("Created instance {} with {} processing units".format(
+        instance_id, instance.processing_units))
+
+
+# [END spanner_create_instance_with_processing_units]
+
+
 # [START spanner_create_database]
 def create_database(instance_id, database_id):
     """Creates a database and tables for sample data."""

samples/samples/snippets_test.py

@@ -53,6 +53,7 @@ def cleanup_old_instances(spanner_client):
 
 
 INSTANCE_ID = unique_instance_id()
+LCI_INSTANCE_ID = unique_instance_id()
 DATABASE_ID = unique_database_id()
 CMEK_DATABASE_ID = unique_database_id()
 
@@ -81,6 +82,14 @@ def test_create_instance(spanner_instance):
     spanner_instance.reload()
 
 
+def test_create_instance_with_processing_units(capsys):
+    processing_units = 500
+    snippets.create_instance_with_processing_units(LCI_INSTANCE_ID, processing_units)
+    out, _ = capsys.readouterr()
+    assert LCI_INSTANCE_ID in out
+    assert "{} processing units".format(processing_units) in out
+
+
 def test_create_database(database):
     # Reload will only succeed if the database exists.
     database.reload()