@Test
public void testNestedSub() {

	String systemKey2 = "testSystemKey2";
	String oldSystemValue = System.setProperty(systemKey2, _SYSTEM_KEY);
	try {
		Assert.assertEquals(
			_SYSTEM_VALUE,
			InterpolationUtil.substVars("${${" + systemKey2 + "}}"));
	}
	finally {
		if (oldSystemValue == null) {
			System.clearProperty(systemKey2);
		}
		else {
			System.setProperty(systemKey2, _oldSystemValue);
		}
	}
}