/** Tests that sealing mutliple times does not cause trouble. */
@Test
public final void multiSealing() {
sealable.seal();
sealable.seal();
assertTrue("A Sealable should be sealed after seal().", sealable.isSealed());
}
/** Tests that the instance is unsealed in the beginning. */
@Test
public final void initiallyUnsealed() {
assertFalse("A Sealable should not be sealed after creation.", sealable.isSealed());
}