Add mockResponseOnce

[gsasouza]

Add a function that allow to change mock return in each test.

Use case:

• I have a query for user login and i need to test success and some fail tests, then in each test the returned value will be different.

Proposal:

• I'm thinking in something like this package function mockResponseOnce.

[robrichard]

I think you can do this without changes to this library. You can write a function for your network layer that returns different invocations of getNetworkLayer

Network.create((operation, variables) => {
  if (variables.email === "failure-test@example.com") {
    // mock failed login test case
    return getNetworkLayer({
      schema,
      mocks: {
        User: () => {
          throw new Error("login failed");
        }
      }
    })(operation, variables);
  }
  // mock successful login test case
  return getNetworkLayer({
    schema,
    mocks: {
      User: () => ({
        id: "123"
      })
    }
  })(operation, variables);
});