Testing: Add a fake implementation of TraceService.

[songy23]

This fake server will be used to test against the clients in #1476.

Equivalent to https://github.com/census-ecosystem/opencensus-go-exporter-ocagent/blob/master/mock_agent_test.go.

[codecov-io]

Codecov Report

Merging #1481 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #1481   +/-   ##
=========================================
  Coverage     82.45%   82.45%           
  Complexity     1590     1590           
=========================================
  Files           243      243           
  Lines          7493     7493           
  Branches        702      702           
=========================================
  Hits           6178     6178           
  Misses         1099     1099           
  Partials        216      216

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[bogdandrutu]

Couple of things:

1. I see no intention to publish this to the users.
2. Why do we not have the Fake implementation in the test dir?

[songy23]

@bogdandrutu I considered putting this fake server under io.opencensus.testing initially. A few concerns about doing so:

1. This will add io.grpc and io.opencensus.proto dependencies to io.opencensus.testing.
2. We have to make the fake server implementation public, while I don't think it will be useful outside the ocagent exporter package.

That being said, I agree that there's no need to include the fake server in the ocagent-exporter artifact. I've moved it to io.opencensus.testing.

[bogdandrutu]

@songy23 my suggestion was to have it in the src/test/java instead of src/main/java. What do you think?

[songy23]

my suggestion was to have it in the src/test/java instead of src/main/java. What do you think?

SGTM, updated. (though it's a bit strange to have tests for a class under test directory.)

[bogdandrutu]

I agree with the fact that tests for test classes is strange; we can move it to the main later but I don't think this should be present in the artifact that gets exported to maven central for example even if this is package protected.

[songy23]

we can move it to the main later but I don't think this should be present in the artifact that gets exported to maven central for example even if this is package protected.

Make sense to me.