### Question:
EnvironmentVariableConfiguration implements Configuration { @Override public String getPropertyValue(String key) { if (Strings.isNullOrEmpty(key)) { _logger.warn("ENV key is null or empty!"); return null; } String value = System.getProperty(key); return value; }  @Override String getPropertyValue(String key);  }### Answer:
@Test public void testGetPropertyValue() { EnvironmentVariableConfiguration configuration = new EnvironmentVariableConfiguration(); assertNull(configuration.getPropertyValue(null)); assertNull(configuration.getPropertyValue("")); assertNull(configuration.getPropertyValue("test")); assertEquals("HotSpot 64-Bit Tiered Compilers", configuration.getPropertyValue("sun.management.compiler")); }