Tests valid_number_step() with offset.
function testNumberStepOffset() {
// Try obvious fits.
$this
->assertTrue(valid_number_step(11.3, 10.3, 1));
$this
->assertTrue(valid_number_step(100, 10, 50));
$this
->assertTrue(valid_number_step(-100, 90 / 7, -10));
$this
->assertTrue(valid_number_step(2 / 7 + 5 / 9, 1 / 7, 5 / 9));
// Ensure a small offset is still invalid.
$this
->assertFalse(valid_number_step(10.3, 10.3, 0.0001));
$this
->assertFalse(valid_number_step(1 / 5, 1 / 7, 1 / 11));
// Try negative values and offsets.
$this
->assertFalse(valid_number_step(1000, 10, -5));
$this
->assertFalse(valid_number_step(-10, 4, 0));
$this
->assertFalse(valid_number_step(-10, 4, -4));
}