"no exported member 'mockLogger'" error when mocking the library in TypeScript

[simonespa]

Context

I'm using this library to send metrics via the metricScope and I need to test the functionality. To do so I'm following the example described here https://github.com/awslabs/aws-embedded-metrics-node/blob/master/examples/testing/tests/module.jest.test.js.

The project is written in TypeScript and I use jest for unit testing.

Issue

This example https://github.com/awslabs/aws-embedded-metrics-node/blob/master/examples/testing/tests/module.jest.test.js fails in a TypeScript context with the following error:

Module '"aws-embedded-metrics"' has no exported member 'mockLogger'.ts(2305)

Question

• How do I expose the mockLogger to the test function without making TypeScript complain?
• Is there a different approach to mock the logger and expose it to the test?

[simonespa]

My workaround to make TypeScript happy was to extend the definition of the library by declaring the following:

declare module 'aws-embedded-metrics' {
  const mockLogger: {
    setNamespace: (value: string) => MetricsLogger;
    setDimensions: (dimensionSet: Record<string, string>) => MetricsLogger;
    setProperty: (key: string, value: unknown) => MetricsLogger;
    putMetric: (key: string, value: number, unit?: Unit | string) => MetricsLogger;
  };
}

By doing so I can use the mockLogger object returned by the stubbed library.

[simonespa]

I also tried other approaches to pass the "mockLogger" without being part of the aws-embedded-metrics to avoid any TypeScript complaint. Unfortunately, the fact that Jest hoists the jest.mock definition doesn't help.