We need to write some tests to prove the Jaeger Exporter can correctly export a batch of spans, which address [this comment](https://github.com/open-telemetry/opentelemetry-go/pull/1673#discussion_r590636247) Possible steps: - [ ] Fix the typo of `testCollectorEnpoint` to `testCollectorEndpoint` - [ ] Refactor `testCollectorEndpoint` to record all the `gen.Batch` that was exported. - [ ] Check the correctness of `gen.Batch`.