public function testIsNegative() { $m1 = new Money(-12, 'EUR'); $m2 = new Money(0, 'EUR'); $m3 = new Money(12, 'EUR'); $this->assertTrue($m1->isNegative()); $this->assertFalse($m2->isNegative()); $this->assertFalse($m3->isNegative()); }