Add opsworks app mocks (#1481)

* Add implementation for OpsWorks create_app and describe_apps

* Fix the name of the test

* Add some more exception tests

tests/test_opsworks/test_apps.py

@@ -0,0 +1,102 @@
+from __future__ import unicode_literals
+import boto3
+from freezegun import freeze_time
+import sure  # noqa
+import re
+
+from moto import mock_opsworks
+
+
+@freeze_time("2015-01-01")
+@mock_opsworks
+def test_create_app_response():
+    client = boto3.client('opsworks', region_name='us-east-1')
+    stack_id = client.create_stack(
+        Name="test_stack_1",
+        Region="us-east-1",
+        ServiceRoleArn="service_arn",
+        DefaultInstanceProfileArn="profile_arn"
+    )['StackId']
+
+    response = client.create_app(
+        StackId=stack_id,
+        Type="other",
+        Name="TestApp"
+    )
+
+    response.should.contain("AppId")
+
+    second_stack_id = client.create_stack(
+        Name="test_stack_2",
+        Region="us-east-1",
+        ServiceRoleArn="service_arn",
+        DefaultInstanceProfileArn="profile_arn"
+    )['StackId']
+
+    response = client.create_app(
+        StackId=second_stack_id,
+        Type="other",
+        Name="TestApp"
+    )
+
+    response.should.contain("AppId")
+
+    # ClientError
+    client.create_app.when.called_with(
+        StackId=stack_id,
+        Type="other",
+        Name="TestApp"
+    ).should.throw(
+        Exception, re.compile(r'already an app named "TestApp"')
+    )
+
+    # ClientError
+    client.create_app.when.called_with(
+        StackId="nothere",
+        Type="other",
+        Name="TestApp"
+    ).should.throw(
+        Exception, "nothere"
+    )
+
+@freeze_time("2015-01-01")
+@mock_opsworks
+def test_describe_apps():
+    client = boto3.client('opsworks', region_name='us-east-1')
+    stack_id = client.create_stack(
+        Name="test_stack_1",
+        Region="us-east-1",
+        ServiceRoleArn="service_arn",
+        DefaultInstanceProfileArn="profile_arn"
+    )['StackId']
+    app_id = client.create_app(
+        StackId=stack_id,
+        Type="other",
+        Name="TestApp"
+    )['AppId']
+
+    rv1 = client.describe_apps(StackId=stack_id)
+    rv2 = client.describe_apps(AppIds=[app_id])
+    rv1['Apps'].should.equal(rv2['Apps'])
+
+    rv1['Apps'][0]['Name'].should.equal("TestApp")
+
+    # ClientError
+    client.describe_apps.when.called_with(
+        StackId=stack_id,
+        AppIds=[app_id]
+    ).should.throw(
+        Exception, "Please provide one or more app IDs or a stack ID"
+    )
+    # ClientError
+    client.describe_apps.when.called_with(
+        StackId="nothere"
+    ).should.throw(
+        Exception, "Unable to find stack with ID nothere"
+    )
+    # ClientError
+    client.describe_apps.when.called_with(
+        AppIds=["nothere"]
+    ).should.throw(
+        Exception, "nothere"
+    )