TypeError: Cannot read property 'SharedIniFileCredentials' of undefined

## Background
I had one small issue when integrating `sls-test-tools` into an integration test pack.

When running the test spec against a stack I was getting the following error:

Background to this, previous to adding the integration test suite we had added a unit test suite with mocks for the AWS SDK following [this method](https://dev.to/elthrasher/mocking-aws-with-jest-and-typescript-199i).

After some experimentation, it seemed the AWS Mocks file for the unit tests was being included in the integration test run, even though our route to the tests was very explicit.

## Solution

The most straightforward solution was to have two `jest.config.js`:

- `jest.integration.config.js`
- `jest.unit.config.js`

In integration test config excludes the mocks:

```Javascript
modulePathIgnorePatterns: [
"__mocks__"
]
```
Then we specified which config to run in the `package.json`:

```json
"scripts": {
"test:unit": "jest \"src/.*.test.ts\" --config=jest.unit.config.js",
"test:integration": "jest \"__tests__/integration/.*.test.js\" --config=jest.integration.config.js"
}
```
Hope this helps anyone that may run into a similar issue, or if there is a better way of dealing with this?