tests: add test for DefaultAuthorizers not a string in API (#2313)

In issue #1245, we had a cases were SAM would fail due to improper validation.
In updating #1286, I noticed this was patched in #1774 but we only added tests
for AWS::Serverless::StateMachine. This commit adds an additional test to cover
AWS::Serverless::Api.

Co-authored-by: Jacob Fuss <[email protected]>

Author: jfuss

tests/translator/input/error_default_authorizer_should_be_string_in_api.yaml

@@ -0,0 +1,30 @@
+AWSTemplateFormatVersion: "2010-09-09"
+Transform: "AWS::Serverless-2016-10-31"
+
+Resources:
+  MyApi:
+    Type: "AWS::Serverless::Api"
+    Properties:
+      StageName: Prod
+      Auth:
+        DefaultAuthorizer: !Ref MyCognitoAuth
+        Authorizers:
+          MyCognitoAuth:
+            UserPoolArn: arn:aws:1
+            Identity:
+              Header: MyAuthorizationHeader
+              ValidationExpression: myauthvalidationexpression
+
+  MyFunction:
+    Type: AWS::Serverless::Function
+    Properties:
+      CodeUri: s3://sam-demo-bucket/thumbnails.zip
+      Handler: index.handler
+      Runtime: nodejs8.10
+      Events:
+        Api:
+          Type: Api
+          Properties:
+            RestApiId: !Ref MyApi
+            Path: /
+            Method: get

tests/translator/output/error_default_authorizer_should_be_string_in_api.json

@@ -0,0 +1,3 @@
+{
+    "errorMessage": "Invalid Serverless Application Specification document. Number of errors found: 1. Resource with id [MyApi] is invalid. DefaultAuthorizer is not a string."
+}