code: public void loadSystemProperties(String configurationKey) {
          String propertyRef = getProperty(configurationKey);
          if (propertyRef == null) {
              return;
          }
  
          if (propertyRef.startsWith("env:")) {
              propertyRef = propertyRef.substring(4);
              propertyRef = System.getenv(propertyRef);
          }
  
          if (!propertyRef.startsWith("/")) {
              propertyRef = "/" + propertyRef;
          }
          try {
              URL url = getClass().getResource(propertyRef);
              if (url == null) {
                  url = new URL(propertyRef);
              }
              Properties props = System.getProperties();
              props.load(url.openStream());
              System.setProperties(props);
          }
          catch (IOException exc) {
              throw new TestContainerException(exc);
          }
      }
docs: Loads system properties from the given configuration key.
  <p>
  If this configuration key has no value, then this method has no effect.
  <p>
  If the value starts with {@code env:}, this prefix is stripped and the remainder is taken to
  be an environment variable. The value is then replaced by the value of the environment
  variable.
  <p>
  This value is now interpreted as a classpath resource and converted to a URL. If the value
  has no matching classpath resource, the value itself is interpreted as a URL.
  <p>
  Finally, properties are loaded from this URL and merged into the current system properties.
  
  @param configurationKey
  configuration key, the value defining a property source