TDD for Euler Problem #4
First of all, your PalindromeChecker does not contain any state, it is a simple input --> output operation not depending on outer factors. This makes it an ideal candidate for being a static method.

Your naming is okay overall, but I would use the name Palindromes for your class.



String str = new Integer(input).toString();


It is better to use String.valueOf here. There's no need to create an Integer object.



for (int j = 999; j&gt;100; j--){


Technically, you're off by one here. You're missing the case when j == 100, which is also a three-digit number (the same goes for i btw).

Correct would be (also with improved spacing)

for (int j = 999; j &gt;= 100; j--) {




So, here's how I would make your class:

public class Palindromes {

    public static boolean isPalindrome(int input) {
        String str = String.valueOf(input);
        int len = str.length();

        for(int i = 0; i &lt; Math.ceil(len/2.0); i++) {
            if (str.charAt(i) != str.charAt(len - i - 1)) {
                return false;
            }
        }
        return true;
    }

}




All your test cases contains pretty much the same code, but with different parameters.

With the change to a static method, the test cases will look more like:

assertFalse("10 failed", Palindromes.isPalindrome(10));


This is ideal for a Parameterized test, which will make it significantly easier to add more tests.

@RunWith(Parameterized.class)
public class PalindromeTest {
    @Parameters
    public static Collection&lt;Object[]&gt; data() {
        return Arrays.asList(new Object[][] {     
                 { 10, false },
                 { 100, false },
                 { 909, true },
                 ...
           });
    }

    private final int input;

    private final boolean expectedPalindrome;

    public PalindromeTest(int input, boolean expectedPalindrome) {
        this.input = input;
        this.expectedPalindrome = expectedPalindrome;
    }

    @Test
    public void test() {
        assertEquals("Failed for " + input,
            expectedPalindrome, Palindromes.isPalindrome(input));
    }
}