I'm seeing an issue in Jest where calling jest.clearAllMocks() inside a beforeEach callback seems to wipe out calls to a mocked function that are made not before but WITHIN a specific test. I can repro it as follows:

THIS PASSES:

__tests__/testy.test.js

const AWS = require("aws-sdk");
const { handler } = require("../index.js");

describe("Lambda function tests", () => {
    it("sent the expected CSV data to S3", async () => {
        // RUN THE LAMBDA, await completion
        await handler();
        // The S3 constructor should have been called during Lambda execution
        expect(AWS.S3).toHaveBeenCalled();
    });
});

THIS GIVES ME A FAILURE:

__tests__/testy.test.js

const AWS = require("aws-sdk");
const { handler } = require("../index.js");

describe("Lambda function tests", () => {
    beforeEach(() => {
        jest.clearAllMocks();
    });
    it("sent the expected CSV data to S3", async () => {
        // RUN THE LAMBDA, await completion
        await handler();
        // The S3 constructor should have been called during Lambda execution
        expect(AWS.S3).toHaveBeenCalled();
    });
});

The failure message in the console:

expect(jest.fn()).toHaveBeenCalled()

    Expected number of calls: >= 1
    Received number of calls:    0

I'm using jest version 27.4.3 in Node v14.18.1. In case it matters, I'm mocking aws-sdk like this:

__mocks__/aws-sdk.js

const AWS = jest.createMockFromModule("aws-sdk");

AWS.S3 = jest.fn().mockImplementation(() => ({
    upload: jest.fn(() => ({ promise: jest.fn() })),
    headObject: jest.fn(() => ({
        promise: jest.fn(() => ({ ContentLength: 123 })),
    })),
}));

module.exports = AWS;

What could be happening here?