100coverage.java

import org.junit.Test;

import static org.junit.Assert.assertEquals;

public class ExampleTest {

  /*
      Sometimes(*) 100% line coverage is not enough
  */

  @Test
  public void one_case_that_covers_all_the_lines() {
    assertEquals("50.0 %", this.formattedPercentage(5, 10));
  }


  private String formattedPercentage(double x, double y) {
    return  String.valueOf((x / y) * 100) + " %";  //if y == 0 it fails, no test covers this
  }

}
-// (*) Achieving 100% coverage can be really hard. You need to think about the ROI (economic!) of the tests you are writing
-// Don´t think about "line coverage", think about 100% of input/output combination cases 

	@Test
	public void one_case_that_covers_all_the_lines() {
		assertEquals("50.0 %", this.formattedPercentage(5, 10));
	}

	@Test(expected = ArithmeticException.class)
	public void divide_by_zero() {
		this.formattedPercentage(5, 0);
	}

	private String formattedPercentage(double x, double y) throws ArithmeticException {
		if (y == 0) {
			throw new ArithmeticException();
		}
		return String.valueOf((x / y) * 100) + " %"; // if y == 0 it fails, no test covers this
	}