public void doRunSharedInitializer(SpockExecutionContext context, SpecInfo spec) {
    runSharedInitializer(context, spec.getSuperSpec());
    if (context.getErrorInfoCollector().hasErrors()) return;
    invoke(context, context.getCurrentInstance(), spec.getSharedInitializerMethod());
  }
Executes a single Spec. Notifies its supervisor about overall execution
progress and every invocation of Spec code.
Supervisor also determines the error strategy.

@author Peter Niederwieser
spock-core/src/main/java/org/spockframework/runtime/PlatformSpecRunner.java