How to Test Package Main in Go

There are a few things to get right when trying to test the main package in Go. This is a result of package naming rules and where files need to be located. My attempts from other testing frameworks (such as Python) led me to error messages such as:

• cannot find package "mypackage" in any of: /first/path/ (from $GOROOT), /second/path/ (from $GOPATH)
• can't load package: package mypackage: found packages main (mypackage.go) and mypackage (mypackage_test.go) in /project/path
• ./mypackage_test.go:4: import "path/to/mypackage" while compiling that package (import cycle)

However, it should be possible to resolve all these errors by following this checklist:

• An executable package must have the name main (so package main).
• The name of the code file can be as desired, so example.go in this example.
• The name of the test file should have _test.go at the end, so example_test.go.
• The test file should be in the same directory as the code file.
• The package name of the test file must also be package main.
• There is no need to import the code in the test file as everything is in the same package.

You don't necessarily need to have these files in a subdirectory of your project; you can have all files in the root directory of the project.