Verify that all packages have tests

[yurishkuro]

Add make nocover target (that also runs as part of make cover) that checks all directories that have Go files but no test files and fails if such directories don't also have .nocover marker, which indicates that the directories are silently excluded from code coverage. If .nocover marker is found, it is printed, so that it's easy to find directories without code coverage. Directories with main.go are ignored.

The script found a number of directories:

• Some of them have only type definitions, so an empty_test.go file was added to those
• Some were legitimately excluded due to external requirements, like the gocql module. A .nocover file was added to those dirs with an explanation.
• Four directories were still missing tests, even though it should be possible to add coverage. Those were also marked with .nocover file containing the word FIXME.

The current output of nocover command looks like this:

$ make nocover
Verifying that all packages have test files to count in coverage
Package excluded from coverage: ./cmd/agent/app/httpserver/thrift-0.9.2
  reason: Thrift-generated files
Package excluded from coverage: ./cmd/flags
  reason: FIXME
Package excluded from coverage: ./pkg/cassandra/config
  reason: requires connection to Cassandra
Package excluded from coverage: ./pkg/cassandra/gocql
  reason: requires connection to Cassandra
Package excluded from coverage: ./pkg/cassandra/gocql/testutils
  reason: FIXME
Package excluded from coverage: ./pkg/es
  reason: FIXME
Package excluded from coverage: ./pkg/es/config
  reason: requires connection to Elasticsearch
Package excluded from coverage: ./pkg/version
  reason: FIXME

Fixes #168

Signed-off-by: Yuri Shkuro ys@uber.com

[coveralls]

Coverage remained the same at 100.0% when pulling b4e974c on fix-168 into 32bc1b7 on master.