public TestRunner addExternalContext(ExternalContext externalContext) {
    Preconditions.checkNotNull(externalContext);
    this.externalContext = externalContext;
    return this;
  }
Passes the user provided external context to {@link LocalApplicationRunner}

@param externalContext external context provided by user
@return this {@link TestRunner}
samza-test/src/main/java/org/apache/samza/test/framework/TestRunner.java