Understanding Jest's beforeEach and test.each

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Introduction

Jest's [beforeEach](prompt://ask_markdown?question=beforeEach) function is used to run a specific setup code before each test in a test file. This ensures that each test starts with a clean state.
[test.each](prompt://ask_markdown?question=test.each) in Jest allows you to run the same test with different data sets. This is useful for parameterized testing where the same logic needs to be tested with various inputs.
Using beforeEach helps in avoiding code repetition by setting up common test conditions once for all tests.
test.each can be used with arrays of arrays or arrays of objects to provide different sets of parameters to the test function.
Both beforeEach and test.each can handle asynchronous code, making them versatile for various testing scenarios.

Purpose: beforeEach runs a function before each test in a file, ensuring a clean state for each test.
Usage: Commonly used to initialize or reset data, such as databases or mock objects, before each test.
Asynchronous Support: Can handle asynchronous code by returning a promise or using the done callback.
Example: beforeEach(() => { [initializeCityDatabase](prompt://ask_markdown?question=initializeCityDatabase)(); });
Scoping: beforeEach inside a describe block only applies to tests within that block.

Purpose: test.each allows running the same test with different data sets, useful for parameterized testing.
Usage: Can be used with arrays of arrays or arrays of objects to provide different sets of parameters.
Example: test.each([[1, 1, 2], [1, 2, 3], [2, 1, 3]])('.add(%i, %i)', (a, b, expected) => { expect(a + b).toBe(expected); });
Asynchronous Support: The test function can be asynchronous, returning a promise or using async/await.
Flexibility: Supports various data formats and can generate unique test titles using printf-style formatting.

Setup: beforeEach and [beforeAll](prompt://ask_markdown?question=beforeAll) are used for setup tasks before tests run.
Teardown: [afterEach](prompt://ask_markdown?question=afterEach) and [afterAll](prompt://ask_markdown?question=afterAll) are used for cleanup tasks after tests run.
Example: beforeEach(() => { initializeCityDatabase(); }); afterEach(() => { [clearCityDatabase](prompt://ask_markdown?question=clearCityDatabase)(); });
Asynchronous Support: Both setup and teardown functions can handle asynchronous code.
Scoping: Setup and teardown functions inside a describe block only apply to tests within that block.

Global Scope: beforeEach and afterEach at the top level apply to all tests in the file.
describe block Scope: Hooks inside a describe block only apply to tests within that block.
Nested Describe Blocks: Hooks in nested describe blocks follow a hierarchical order of execution.
Example: describe('outer', () => { beforeEach(() => { /* setup */ }); describe('inner', () => { beforeEach(() => { /* inner setup */ }); }); });
Order: Top-level hooks run before nested hooks, ensuring proper setup and teardown.

Describe Handlers: Jest executes all describe handlers before running any tests.
Hook Order: beforeAll runs before beforeEach, and afterEach runs before afterAll.
Example: beforeAll(() => console.log('1 - beforeAll')); beforeEach(() => console.log('1 - beforeEach')); test('', () => console.log('1 - test'));
Nested Hooks: Hooks in nested describe blocks follow a hierarchical order.
execution flow: Ensures proper setup and teardown, avoiding interference between tests.