Given a String, return a boolean if it is a number
Instead of reading the output of those print statements, it's better write proper unit tests to verify your implementation:

@Test
public void testValidInteger() {
    assertTrue(isNumber("123"));
}

@Test
public void testValidStartsWithDecimal() {
    assertTrue(isNumber(".123"));
}

@Test
public void testValidNegativeStartsWithDecimal() {
    assertTrue(isNumber("-.123"));
}

@Test
public void testValidDecimal() {
    assertTrue(isNumber("1.23"));
}

@Test
public void testValidMinusZero() {
    assertTrue(isNumber("-0"));
}


Your implementation passes all these, which is good. I would add at least two more:

@Test
public void testValidEndsWithDecimal() {
    assertTrue(isNumber("123."));
}

@Test
public void testValidDecimalLooooong() {
    assertTrue(isNumber("1.2311111111111111111111111111111111111111111"));
}


The second passes but the first doesn't and maybe it should, no?

For testing cases of non-numbers:

@Test
public void testNotValid() {
    assertFalse(isNumber("-."));
    assertFalse(isNumber(".-"));
    assertFalse(isNumber("12.34.56"));
    assertFalse(isNumber("-"));
    assertFalse(isNumber("12$%^&amp;*#"));
    assertFalse(isNumber("hello"));
    assertFalse(isNumber("   "));
    //assertFalse(isNumber(""));
}


It would be good to split these to individual cases as I did for the valid cases. I leave that for you as an exercise. I added some more cases here too, and unfortunately the one with empty string doesn't pass. I think that's a bug.

As per your implementation, it seems more complicated than it needs to be.
Most importantly, I'm wondering if the interviewer would consider regular expressions as "parse function". If not, then the implementation can be simplified:

public static boolean isNumber(String toTest) {
    return toTest.matches("[+-]?(\\d*\\.?\\d+)|(\\d+\\.?\\d*)");
}


This passes all the above tests. To correct and simplify your implementation, it should not be terribly difficult to implement the logic of the regular expression.