Integration Tests Not Properly Mocked

I followed the integration tests example pattern in my own app.

```
// mock the datasources' underlying fetch methods, whether that's a REST
// lookup in the RESTDataSource or the store query in the Sequelize datasource
launchAPI.get = jest.fn(() => [mockLaunchResponse]);
```

However I noticed it was still making api calls to the rest endpoint. I then cloned this repo turned off my wifi and ran the integration tests and sure enough I got an error.

```
errors": Array [
+ Object {
+ "extensions": Object {
+ "code": "INTERNAL_SERVER_ERROR",
+ "exception": Object {
+ "code": "ENOTFOUND",
+ "errno": "ENOTFOUND",
+ "message": "request to https://api.spacexdata.com/v2/launches?flight_number=30 failed, reason: getaddrinfo ENOTFOUND api.spacexdata.com api.spacexdata.com:443",
+ "type": "system",
+ },
},
- "rocket": Object {
- "type": "FT",
- },
+ "locations": Array [
+ Object {
+ "column": 3,
+ "line": 2,
+ },
+ ],
+ "message": "request to https://api.spacexdata.com/v2/launches?flight_number=30 failed, reason: getaddrinfo ENOTFOUND api.spacexdata.com api.spacexdata.com:443",
+ "path": Array [
+ "launch",
+ ],
```

This tells me that `launchAPI.get` is not being properly mocked. Which I think would make sense as there is no `launchAPI.get` however there is a `launchAPI.prototype.get` however that doesn't seem to work when I change the tests to that.

Any ideas?

Start by running the integration tests with networking disabled and inspect the example that assigns launchAPI.get, then trace which RESTDataSource method handles the launch lookup. The issue names no files or test command; done should mean the integration tests pass offline without requesting api.spacexdata.com and still return the expected rocket data.

Written by the indexing model from the issue text.