go build works but go test does not

Below is my project structure:
<pre>
/user/home/go/src/github.com/my_go_proj
/main.go
/mypackage
/service.go
/service_test.go

GOPATH points to /user/home/go
cd /user/home/go/src/github.com/my_go_proj
go build ---> This works and creates the my_go_proj executable.
go test
? github.com/my_go_proj [no test files]
go test github.com/my_go_proj/mypackage
go build gopkg.in/tomb.v2: no buildable Go source files in
FAIL github.com/my_go_proj/mypackage [build failed]

go test ./...
? github.com/my_go_proj [no test files]
go build gopkg.in/tomb.v2: no buildable Go source files in
FAIL github.com/my_go_proj/mypackage [build failed]

</pre>

How do I run go test to run the service_test.go test inside mypackage?

Update: updated the behaviour for go test ./...

To test all subdirectories use:

$ go test ./...

From the Relative import paths section of the Command go documentation:

> Relative patterns are also allowed, like go test ./... to test all subdirectories. See 'go help packages' for details on the pattern syntax.

The problem was with the directory structure. My project source should be in $GOPATH. But it was inside $GOPATH/src.

Incorrect /user/home/go/src/github.com/my_go_proj <br>
Correct /user/home/go/github.com/my_go_proj