Added non existant parameter test + needed error responses

moto/ssm/responses.py

@@ -49,7 +49,11 @@ class SimpleSystemManagerResponse(BaseResponse):
         result = self.ssm_backend.get_parameter(name, with_decryption)
 
         if result is None:
-            return '', dict(status=400)
+            error = {
+                '__type': 'ParameterNotFound',
+                'message': 'Parameter {0} not found.'.format(name)
+            }
+            return json.dumps(error), dict(status=400)
 
         response = {
             'Parameter': {

tests/test_ssm/test_ssm_boto3.py

@@ -1,6 +1,7 @@
 from __future__ import unicode_literals
 
 import boto3
+import botocore.exceptions
 import sure   # noqa
 
 from moto import mock_ssm
@@ -85,6 +86,20 @@ def test_get_parameter():
     response['Parameter']['Type'].should.equal('String')
 
 
+@mock_ssm
+def test_get_nonexistant_parameter():
+    client = boto3.client('ssm', region_name='us-east-1')
+
+    try:
+        client.get_parameter(
+            Name='test_noexist',
+            WithDecryption=False)
+        raise RuntimeError('Should of failed')
+    except botocore.exceptions.ClientError as err:
+        err.operation_name.should.equal('GetParameter')
+        err.response['Error']['Message'].should.equal('Parameter test_noexist not found.')
+
+
 @mock_ssm
 def test_describe_parameters():
     client = boto3.client('ssm', region_name='us-east-1')