/** @depends testConstructEmpty */
public function testValidity()
{
$tax = new Tax("Cat", "Label", stdtimefstr("2001-01-01 00:00:00"), 0.2);
$this->assertTrue($tax->isValid(stdtimefstr("2001-01-01 00:00:00")), "Tax recognised invalid at change date");
$this->assertTrue($tax->isValid(stdtimefstr("2001-01-02 00:00:00")), "Tax recognised invalid after change date");
$this->assertFalse($tax->isValid(stdtimefstr("2000-01-01 00:00:00")), "Tax recognised valid before change date");
}