### Question:
SystemPropertyUtil { public static String get(String key) { return get(key, null); } private  SystemPropertyUtil(); static boolean contains(String key); static String get(String key); static String get(final String key, String def); static int getInt(String key, int def);  }### Answer:
@Test(expectedExceptions = NullPointerException.class) public void testGetWithKeyNull() { SystemPropertyUtil.get(null, null); }
@Test(expectedExceptions = IllegalArgumentException.class) public void testGetWithKeyEmpty() { SystemPropertyUtil.get("", null); }
@Test public void testGetDefaultValueWithPropertyNull() { assertEquals("default", SystemPropertyUtil.get("key", "default")); }
@Test public void testGetPropertyValue() { System.setProperty("key", "value"); assertEquals("value", SystemPropertyUtil.get("key")); }