mocktracer/mocktracer.go
func (t *MockTracer) StartSpan(operationName string, opts ...opentracing.StartSpanOption) opentracing.Span {
	sso := opentracing.StartSpanOptions{}
	for _, o := range opts {
		o.Apply(&sso)
	}
	return newMockSpan(t, operationName, sso)
}
func (t *MockTracer) StartSpan(operationName string, opts ...opentracing.StartSpanOption) opentracing.Span {
	sso := opentracing.StartSpanOptions{}
	for _, o := range opts {
		o.Apply(&sso)
	}
	return newMockSpan(t, operationName, sso)
}
// StartSpan belongs to the Tracer interface.