Eclipse(java testing) - terminate mutant version

I am a learner on the Coursera "Introduction to Software Testing" course. I am submitting my unit test assignment but the grader output on the Coursera site shows me this:

mutant1: -0.020833333333333332 *** Learner did not properly terminate mutant version! ***
mutant10: -0.020833333333333332 *** Learner did not properly terminate mutant version! ***
mutant15: -0.020833333333333332 *** Learner did not properly terminate mutant version! ***
mutant18: -0.020833333333333332 *** Learner did not properly terminate mutant version! ***
mutant2: -0.020833333333333332 *** Learner did not properly terminate mutant version! ***
mutant21: -0.020833333333333332 *** Learner did not properly terminate mutant version! ***
mutant23: -0.020833333333333332 *** Learner did not properly terminate mutant version! ***
mutant25: -0.020833333333333332 *** Learner did not properly terminate mutant version! ***
mutant3: -0.020833333333333332 *** Learner did not properly terminate mutant version! ***

Kindly help! I have to submit the assignment to get a certificate.

// Demo.java
import java.util.Scanner;
public class Demo {
public static void main(String[] args) {
// Reading from System.in
Scanner reader = new Scanner(System.in);  
System.out.println("Enter side 1: ");
// Scans the next token of the input as an int.
int side_1 = reader.nextInt();
System.out.println("Enter side 2: ");
// Scans the next token of the input as an int.
int side_2 = reader.nextInt();
System.out.println("Enter side 3: ");
// Scans the next token of the input as an int.
int side_3 = reader.nextInt();
if (isTriangle(side_1, side_2, side_3)) {
System.out.println("This is a triangle.");
}
else {
System.out.println("This is not a triangle.");
}
reader.close();
}
public static boolean isTriangle(double a, double b, double c) {
if ((a + b > c) &&
(a + c > b) && // should be a + c > b
(b + c > a)) {
return true; 
}
return false;
}
}

the testing code is:

import static org.junit.Assert.*;
import org.junit.Test;
public class DemoTest {
@Test
public void triangle_test_1() {
assertTrue(Demo.isTriangle(3,2,4));
}
@Test
public void triangle_test_2() {
assertTrue(Demo.isTriangle(4,3,5));
}
@Test
public void triangle_test_3() {
assertTrue(Demo.isTriangle(5,3,5));
}
@Test
public void triangle_test_4() {
assertTrue(Demo.isTriangle(6,4,5));
}
@Test
public void triangle_test_5() {
assertTrue(Demo.isTriangle(7,5,6));
}
@Test
public void triangle_test_6() {
assertFalse(Demo.isTriangle(13,2,4));
}
@Test
public void triangle_test_7() {
assertFalse(Demo.isTriangle(4,3,15));
}
@Test
public void triangle_test_8() {
assertFalse(Demo.isTriangle(3,22,4));
}
@Test
public void triangle_test_9() {
assertFalse(Demo.isTriangle(24,2,5));
}
@Test
public void triangle_test_10() {
assertFalse(Demo.isTriangle(34,2,4));
}
@Test
public void triangle_test_11() {
assertFalse(Demo.isTriangle(2,10,4));
}
}

Because they created and used mutant versions of the Demo.java. Mutant code is a version of the original code with single syntactical change, like '+' is changed to '-', variable A to variable B, or '>' changed to '>='.

Each of these changes can make the code behave differently from the original code and your test script should detect these changes.

mutant1: -0.020833333333333332 *** Learner did not properly terminate mutant version! ----- means that your test script passed against a mutant code in which it should not, it means that your test script does not cover much of the possible errors in the code.

Try: add input combinations using 1,2,3

This error just means that you didn't write enough unit tests. "Mutant" is a changed code, which is invalid and which should make some of your unit tests fail. So basically this error message says that tests were executed against invalidly changed code and that all passed. So you should add more test to cover all cases.