code: public void startStep(final String parentUuid, final String uuid, final StepResult result) {
          notifier.beforeStepStart(result);
  
          result.setStage(Stage.RUNNING);
          result.setStart(System.currentTimeMillis());
  
          threadContext.start(uuid);
  
          storage.put(uuid, result);
          storage.get(parentUuid, WithSteps.class).ifPresent(parentStep -> {
              synchronized (storage) {
                  parentStep.getSteps().add(result);
              }
          });
  
          notifier.afterStepStart(result);
      }
docs: Start a new step as child of specified parent.
  
  @param parentUuid the uuid of parent test case or step.
  @param uuid       the uuid of step.
  @param result     the step.