tree-gen | Generating Trees with a Space Colonization Algorithm | Learning library

You seem confused about what a module is. The rule of thumb is, one go.mod file equals one module. Go Wiki, gomod:

A module is defined by a tree of Go source files with a go.mod file in the tree's root directory.

Based on your directory tree shown in your question, there is no go.mod file in sight, hence nothing there is a Go module. As a matter of fact, if you attempt running a module-aware command from google-golang or golang-getting-started you'll have:

go: go.mod file not found in current directory or any parent directory; see 'go help modules'

If you want to run all tests from the root of a multi-module repo, as the title of your question says, with Go 1.17 you can:

1. init the sub-modules: