The value of building mock server

inspried by Moco framework

Background

Modern application are more based on components design.In one hand,sharding the application to pieces can bring more agility to app's scability ,but on the others hand ,it also introduce dependency problems to qa ,dev and performance tester.

Introduction

Imagine that you are a automation qa that writing a piece of automation test case to test the api behavior,thus until development deploy their code to testing environment ,qa has no way to test and run their automation code to ensure the automation function is done.

Imagine that you are going to test a 3rd paryty response payload ,that claims "a little" update on their response payload,and you want to ensure our system can work as expected,how to test that?

Imagine that you are are front end engineer that develops a single page + restful application ,how to been unblocked for the frontend work ,and meanwhile backend's coding work is still on going?

Imagine that you are a backend engineer,and you are going to create a service and internally it has dependency to other component,they has their seperate SDLC,how can you test you function based on api specs even other component's api is not ready yet.

Imagine that you are a performance tester,you are going to test the real wold api performance benchmark and this api has 3rd party dependency,like generate UPS shipping label via RPC call.how can you test the performance in our own code as well as to maxisum the situation in production.

The answer is mock server.

defining mock specs

How to define the mock specs depends on the question ,"are we really need to merge our testing date and testing code together?".It depends.

For automation ,as eventually they will remove the mock server to real api endpoint ,thus mock server is just a tempority solution for them to be unblocked ,apparently no need to maintain the mock specs

For performance tests and manully function test,it is all handful work ,no need to code for setting up any mock specs as well

in above two cases ,a UI tooling may sufficient for them to go ahead. like below:

```
{
  "request" :
    {
      "uri" : "/foo",
      "cookies" :
        {
          "login" : "true"
        }
    },
  "response" :
    {
      "body":{
        "text" : "success"
      }
    }
}
```

if in bound request has cookies["login"] equals to true and uri is "/foo" ,then return text "success".

But for develop's integration test,it definitely needs to maintain their mock specs as part of their integration tests,so as to ensure a more safety and standalone environment to have a fine-grain control of their internal code logic.The reason is they are testing their own code logic instead of other component's,thus they need to set up various specs to cover positive ,negative,failover, retry and so on ,to ensure their code is robust enough to cover all aspects in distributing environment.

in above case ,a native language friendly dsl may be a good choice to go,like below:

```
whenRequest().matchUri("/foo").and().matchCookies("login",true).
thenReturn().text("success");
```

Some thoughs

Mock server can only mock the response instead behavior ,for instance if you want to test the subsequent flow to see if the post request has successly add the record into db ,this can not be handled by mock server,should we add this into mock server's scope? this is an open topic to discuss

But by setting up the mock server can help develop to skip the steps to setting preparing data to return expected value and very easy to create a exception response to simulate an error case.

Mock specs is very much bounded to test case it self ,how to manage those mock specs should we open a shared platform or private platform? what is the lifecycle to that?

Conclusion

Mock server becomes more and more important in various company ,ebay,alibaba,baidu and google as e-commerce site has various integration tasks,mock server solve the problem to test the 3rd party api as well as internal api,and easily create various senario to cover the test case But mean while we still see some shortcuts that mock server can not bring ,such as mock behavior,will this be another opptunity?

Jason Cui's Site