This is a rough draft of how we could define mocks in a nice way

0-README.md

API Proposal

I would like to solve the problem of stubs in a way that allows us to easily extend them. I would also like to prevent the stubs to go stale and I would like to have it defined in a central place. Let me show you what I have in mind on the next files.

1-mocks-cluster.jsx

const Cluster = require("#mocks/definitions/cluster");

export function DefaultCluster({ children, applications, clusterProps = {} }) {
  const hostname = "127.12.12.4";
  return (
    <Cluster {...clusterProps}>
      <Node hostname={hostname}>
        {/* My point is we COULD use mechanisms like this, we don't need to. It empowers us IMHO */}
        {React.Children.map(applications(), element =>
          React.cloneElement(element, { hostname })
        )}
      </Node>
      {children}
    </Cluster>
  );
}

export function SingleNodeCluster({ children }) {
  return <DefaultCluster applications={() => children} />;
}

export function TwoNodeCluster({
  firstNodeApplications,
  secondNodeApplications
}) {
  return (
    <DefaultCluster applications={firstNodeApplications}>
      <Node hostname="127.12.12.5">
        {React.Children.map(secondNodeApplications(), element =>
          React.cloneElement(element, { hostname })
        )}
      </Node>
    </DefaultCluster>
  );
}

2-tests-my-test-cy.jsx

const { setStub, setStubWithAdapter } = require("magic-lib");
const DefaultCluster = require("#mocks/default-cluster");
const DefaultApp = require("#mocks/default-app");

describe("Service", () => {
  it("has a started service", () => {
    const stub = setStub(
        <DefaultCluster
          renderApplications={() => <DefaultApp healthStatus="healthy" />}
        />
      )
    );
  });

  it("runs on different services on different nodes", () => {
    const stub = setStub(
        <DefaultCluster
          renderApplications={() => <DefaultApp healthStatus="healthy" />}
        >
          {/* This could also be another import if you use it multiple times */}
          <Node hostname="8.8.8.8">
            <Application id="/my-other-service">
              <Task status="running" />
            </Application>
          </Node>
        </DefaultCluster>
      )
    );
    // ... assertions
  });

  it("runs same service on different nodes in different zones", () => {
    /* Although this seems like a lot of code we could leverage code reuse here.
      What I would like to highlight here is we have the possibility to clearly define
      what we need from a mock in a descriptive way and fine-grained. A first time reader
      will immediately understand which cluster we currently have in our mock. The magic is
      how it happens, not what happens.
    */
    const stub = setStub(
      <Cluster>
        <Node hostname="9.9.9.9" region="us-west-1" zone="us-west-1a">
          <Application id="/my-service">
            <Task status="running" />
          </Application>
        </Node>

        <Node hostname="8.8.8.8" region="eu-west-3" zone="eu-west-3c">
          <Application id="/my-service">
            <Task status="running" />
          </Application>
        </Node>
      </Cluster>
    );
    // ...
  });
});

describe("Possible further extensions", () => {
  // I would like to show you how we could extend this solution in crazy ways.
  // Do we want this? I don't know, but I would love to be enabled to do it if I choose to want it.

  it("could have callbacks", () => {
    const mockApplicationCreation = jest.fn();
    const stub = setStub(
      ({ withApp }) => (
        <DefaultCluster
          renderApplications={() =>
            withApp ? <DefaultApp healthStatus={healthStatus} /> : null
          }
          clusterProps={{
            onAppCreate: mockApplicationCreation
          }}
        />
      ),
      {
        withApp: false
      }
    );

    // Do action that "creates" an app
    expect(mockApplicationCreation).toHaveBeeenCalled();
    mockApplicationCreation.resetMocks();

    stub.setProps({
      withApp: true
    });

    // Do action that "creates" an app, should not send a request because the app already exists
    expect(mockApplicationCreation).not.toHaveBeeenCalled();
  });

  it("could have adapters", () => {
    const setStubForMockServer = setStubWithAdapter("mockserver");
    const setStubForDyson = setStubWithAdapter("dyson");
    const setStubForUnicornSolutionThatSolvesAllOurProblems = setStubWithAdapter(
      "unicorn"
    );
  });
  
  it("could have a dynamic approach to changes", () => {
    const stub = setStub(
      ({ healthStatus }) => (
        <DefaultCluster
          renderApplications={() => <DefaultApp healthStatus={healthStatus} />}
        />
      ),
      {
        healthStatus: "healthy"
      }
    );

    // Cypress assertion that something is like it should be
    stub.setProp({ healthStatus: "unhealthy" });
    // Cypress assertion that something is like it should be

    stub.reset();
  });
});

3-SUMMARY.md

Evaluation

Pros

• We can keep up with new functionality of our services by extending the Cluster component with some additional mocks
• We can easily define defaults in a dynamic and extensible way without having too much magic in place
• We can define different renderers / adapters for different mock servers (mock-server / dyson / ...)
• The solution is very extensible in a lot of directions (making it more dynamic, ...)
• We have one central place to keep up with changes of the APIs we consume not 20, therefore our stubs are not so likely to go stale.
• We can choose the granularity on which we want our mocks to be defined. We can start with very little props and more "scenario"-like outputs and move step by step to the granularity we need

Cons

• JSX always gives the notion of being flexible / changing. It is meant here as only being a static way to describe the current state in the very same file as the tests
• A little bit of magic is involved by this layer of abstraction, at least on how it happens

Implementation

We would need to write a react-renderer. There are a lot of examples that we could take a look at. There is a step by step guide how to do it. If we can find a good abstraction as a basis for defining stubs for different routes as a react element we only need to translate to API calls to the mock server.

Similar API: https://github.com/skidding/react-mock