Like in production code, the way you are using and naming variables in unit tests is important. A magic value is a value that you use in your test without providing any context about it.

This may confuse the other developers as they will wonder why a certain value was used, rather than focusing on the test itself.

When writing unit tests, you should try to express intent as much as possible. Instead of using magic strings, a good approach is to use constants.

Example​

This unit test looks simple, but someone who has not good understanding the production code cannot easily know why the values 0.5 and 10.00 were used.

@Test
void calculateShippingFee_Should_Return_Small_Box_Fee_When_Weight_Lower_Than_1Gk(){

    double fee = ShippingCalculator.calculateShippingFee(0.5);

    assertEquals(10.00, fee);
}

Improved example​

To fix this, you can use constants and name them in a convenient manner. Don’t be afraid of using long constant names to express the intent of your code.

@Test
void calculateShippingFee_Should_Return_Small_Box_Fee_When_Weight_Lower_Than_1Gk(){

    final double LESS_THAN_1KG_WEIGHT = 0.5;
    final double BASE_FEE = 0.5;

    double fee = ShippingCalculator.calculateShippingFee(WEIGHT);

    assertEquals(BASE_FEE, fee);
}