JUnit refresher using a calculator example.

CalculatorTest.java

package com.diamante.example;

import org.assertj.core.api.Assertions;
import org.junit.Test;

import static org.assertj.core.api.Assertions.assertThat;

public class CalculatorTest {

    private final Calculator calculator = new Calculator();

    @Test
    public void sum_returnsFive_whenGivenInputsOfOneAndFour() {
        // Arrange
        double expected = 5;

        // Act
        double result = calculator.sum(1, 4);

        // Assert
        assertThat(result).isEqualTo(expected);
    }

    @Test
    public void minus_returnsFour_whenGivenInputsOfEightAndFour() {
        // Arrange
        double expected = 4;

        // Act
        double result = calculator.minus(8, 4);

        // Assert
        assertThat(result).isEqualTo(expected);
    }

    @Test
    public void product_returnsForty_whenGivenInputsOfTenAndFour() {
        // Arrange
        double expected = 40;

        // Act
        double result = calculator.product(10, 4);

        // Assert
        assertThat(result).isEqualTo(expected);
    }

    @Test
    public void dividend_returnsTen_whenGivenInputsOfFiftyAndFive() {
        // Arrange
        double expected = 10;

        // Act
        double result = calculator.dividend(50, 5);

        // Assert
        assertThat(result).isEqualTo(expected);
    }

    @Test
    public void dividend_returnsInfinity_whenGivenInputsOfTenAndZero() {
        // Arrange
        double expected = Double.POSITIVE_INFINITY;

        // Act
        double result = calculator.dividend(10, 0);

        // Assert
        assertThat(result).isEqualTo(expected);
    }

    @Test
    public void dividend_returnsNaN_whenGivenInputsOfZeroAndZero() {
        // Arrange
        double expected = Double.NaN;

        // Act
        double result = calculator.dividend(0, 0);

        // Assert
        assertThat(result).isEqualTo(expected);
    }
}