Written by hand.
Test case for nested modules without an explicit relationship.
This is nested below the top-level module.

-- .mod --
module example.com/nest/sub
-- .info --
{"Version": "v1.0.0"}
-- go.mod --
module example.com/nest/sub
-- y/y.go --

example.com/downgrade v2.0.0
written by hand

-- .mod --
module example.com/downgrade

require rsc.io/quote v1.5.2
-- .info --

example.com/version v1.0.0
written by hand

-- .mod --
module example.com/version
-- .info --
{"Version":"v1.0.0"}
-- version.go --
package version

example.com/version v1.0.1
written by hand

-- .mod --
module example.com/version
-- .info --
{"Version":"v1.0.1"}
-- version.go --
package version

example.com/latemigrate/v2 v2.0.1
written by hand

This repository migrated to modules in v2.0.1 after v2.0.0 was already tagged.
All versions require rsc.io/quote so we can test downgrades.

v2.0.1 belongs to example.com/latemigrate/v2.

-- .mod --
module example.com/latemigrate/v2

require rsc.io/quote v1.3.0
-- .info --
{"Version":"v2.0.1"}
-- go.mod --
module example.com/latemigrate/v2

require rsc.io/quote v1.3.0

Written by hand.
Test module with a root package added in v1.1.0
and a subpackage added in v1.2.0.

-- .mod --
module example.net/pkgadded

go 1.16
-- .info --
{"Version":"v1.2.0"}
-- go.mod --
module example.net/pkgadded

go 1.16
-- pkgadded.go --
// Package pkgadded was added in v1.1.0.
package pkgadded
-- subpkg/subpkg.go --
// Package subpkg was added in v1.2.0.

Module example.com/retract/self/prerelease is a module that retracts its own
latest version and all other release version.

A pre-release version higher than the highest release version is still
available, and that should be matched by @latest.

-- .mod --
module example.com/retract/self/prerelease

go 1.15

retract v1.0.0 // bad
retract v1.9.0 // self

-- .info --
{"Version":"v1.9.0"}

-- p.go --

example.com/badchain/c v1.0.0

-- .mod --
module example.com/badchain/c
-- .info --
{"Version":"v1.0.0"}
-- c.go --

example.com/version v1.1.0
written by hand

-- .mod --
module example.com/version
-- .info --
{"Version":"v1.1.0"}
-- version.go --
package version

-- .info --
{"Version":"v1.0.0"}
-- .mod --
// Deprecated: in v1.0.0
module example.com/undeprecated

go 1.17
-- go.mod --
// Deprecated: in v1.0.0
module example.com/undeprecated

go 1.17
-- undeprecated.go --
package undeprecated

-- cmd/a/a.go --
package main

import "fmt"