updated test to handle empty response

wiretap will tell you the response is empty.

mock/mock_engine.go

@@ -340,12 +340,12 @@ func (rme *ResponseMockEngine) runWorkflow(request *http.Request) ([]byte, int,
 
 	if len(mock) == 0 {
 		return rme.buildError(
-			404,
-			"No mock generated",
-			fmt.Sprintf("Nothing was generated for the request '%s' with the method '%s'. Check spec response defintions",
+			200,
+			"Response is empty",
+			fmt.Sprintf("Nothing was generated for the request '%s' with the method '%s'. Response is empty",
 				request.URL.Path, request.Method),
-			"not_found",
-		), 404, err
+			"empty",
+		), 200, err
 	}
 
 	return mock, c, nil

mock/mock_engine_test.go

@@ -538,7 +538,7 @@ components:
 	b, status, err := me.GenerateResponse(request)
 	assert.NoError(t, err)
 	assert.Equal(t, 200, status)
-	assert.Equal(t, "", string(b))
+	assert.Equal(t, `{"type":"https://pb33f.io/wiretap/errors#empty","title":"Response is empty (200)","status":200,"detail":"Nothing was generated for the request '/auth' with the method 'POST'. Response is empty"}`, string(b))
 }
 
 // https://github.com/pb33f/wiretap/issues/80