Hailong Wen

Similar to gRPC [gae-interop-testing](https://github.com/grpc/grpc-java/tree/master/gae-interop-testing), we should add integration tests to ensure we do not break compatibility in GAE. This issue comes from [comment](https://github.com/census-instrumentation/opencensus-java/pull/868#issuecomment-348731601) in #868.

Consider using tools to check backward compatibility.

3

This is a part of #858, which introduces some API changes that might break backward compatibility. Besides code review, we need something more automated. Currently I am looking at [JAPICC](https://github.com/lvc/japi-compliance-checker)...

[grpc] java-client -> go-server interop test fail

6

The response by go-server does not contain tag "method". ``` SEVERE: Client received wrong TagContext. Got [Tag{key=TagKey{name=operation}, value=TagValue{asString=interop-test}}, Tag{key=TagKey{name=project}, value=TagValue{asString=open-census}}], want [Tag{key=TagKey{name=method}, value=TagValue{asString=interop.EchoService/echo}}, Tag{key=TagKey{name=operation}, value=TagValue{asString=interop-test}}, Tag{key=TagKey{name=project}, value=TagValue{asString=open-census}}]. ``` With @songy23...