describe('[Unit Under Test]', () => {
  describe('[method/function]', () => {
    it('should [expected behavior] when [condition]', () => {
      // Arrange
      const input = ...;
      const expected = ...;

      // Act
      const result = functionUnderTest(input);

      // Assert
      expect(result).toEqual(expected);
    });

    it('should throw [error] when [invalid condition]', () => {
      // Arrange
      const invalidInput = ...;

      // Act & Assert
      expect(() => functionUnderTest(invalidInput))
        .toThrow(ExpectedError);
    });
  });
});

[should/does] [expected behavior] [when/given] [condition]

// Arrange - set up test data and conditions
const input = createTestInput();
const mockService = createMock();

// Act - execute the code under test
const result = await functionUnderTest(input);

// Assert - verify the outcome
expect(result).toEqual(expectedOutput);
expect(mockService.method).toHaveBeenCalledWith(expectedArgs);

describe('User Service', () => {
  describe('when creating a user', () => {
    it('should save the user to the database', () => { });
    it('should send a welcome email', () => { });
    it('should return the created user', () => { });
  });

  describe('when the email is invalid', () => {
    it('should throw a ValidationError', () => { });
  });
});