code: private EmbeddedTomcatConfiguration extractConfiguration(Class<?> testClass, AbstractConfiguration configuration) {
  		final AbstractConfiguration configurationToUse = configuration == null ? findConfiguration(testClass) : configuration;
  
  		if (configurationToUse == null) {
  			return null;
  		}
  
  		if (!(configurationToUse instanceof EmbeddedTomcatConfiguration)) {
  			throw new IllegalTomcatConfigurationException();
  		}
  
  		return (EmbeddedTomcatConfiguration) configurationToUse;
  	}
docs: Try to extract {@link EmbeddedTomcat} configuration from:
  <ul>
  <li>The given {@code configuration} if it is not {@code null}.</li>
  <li>A class field/method annotated with {@link com.github.mjeanroy.junit.servers.annotations.TestServerConfiguration} on given {@code testClass} otherwise.</li>
  </ul>
  
  @param testClass The test class to analyze.
  @param configuration The configuration to use if not {@code null}.
  @return The {@link EmbeddedTomcat} configuration.
  @throws IllegalTomcatConfigurationException If extracted {@code configuration} is not an instance of {@link EmbeddedTomcatConfiguration}.