xxx.go
xxx_test.go
    TestXXX(t *testing.T)
    BenchmarkXXX(t *testing.B)
xxx_integration_test.go
    TestXXX(t *testing.T)
testdata/
    xxx.txt
    xxy.csv

go test
go test -v
go test ./...
go test -run=TestRotate

go test -benchmem -bench=.

go test -cover
go test ./... -coverprofile=coverage.out
go tool cover -func=coverage.out
go tool cover -html=coverage.out

xxx_integration_test.go
    // +build integration
go test -tags=integration

httptest.ResponseRecorder
httptest.Server

https://github.com/golang/mock

https://blog.golang.org/cover