What is a unit test? AAA pattern (Arrange, Act, Assert).

Unit tests & AAA

For What is a unit test? AAA pattern (Arrange, Act, Assert)., interviewers listen for a crisp definition, how the pieces interact in a real system, and one trade-off or failure mode you have seen or would guard against.

@Test
void totalPrice_appliesDiscount() {
  // Arrange
  Cart cart = new Cart().add(100);
  // Act
  int total = cart.totalWithDiscount(10);
  // Assert
  assertEquals(90, total);
}