func (t *MockTracer) FinishedSpans() []*MockSpan {
	t.RLock()
	defer t.RUnlock()
	spans := make([]*MockSpan, len(t.finishedSpans))
	copy(spans, t.finishedSpans)
	return spans
}
func (t *MockTracer) FinishedSpans() []*MockSpan {
	t.RLock()
	defer t.RUnlock()
	spans := make([]*MockSpan, len(t.finishedSpans))
	copy(spans, t.finishedSpans)
	return spans
}
// FinishedSpans returns all spans that have been Finish()'ed since the
// MockTracer was constructed or since the last call to its Reset() method.