$ cat go.work
go 1.20

use (
        .
        ./module1
        ./module2
)
$ tree .
.
├── go.mod
├── go.work
├── module1
│   ├── go.mod
│   ├── package1
│   │   └── source.go
│   ├── package2
│   │   └── source.go
│   └── source.go
├── module2
│   ├── go.mod
│   ├── internal
│   │   └── pkg
│   │       └── source.go
│   └── source.go
├── package1
│   └── source.go
├── package2
│   └── source.go
└── source.go

9 directories, 12 files

$ modlist
example.com/multi
example.com/multi/module1
example.com/multi/module2

$ modlist --packages
example.com/multi
example.com/multi/module1
example.com/multi/module1/package1
example.com/multi/module1/package2
example.com/multi/module2
example.com/multi/module2/internal/pkg
example.com/multi/package1
example.com/multi/package2

$ go test -coverpkg=`modlist -p -e="*internal*" --separator=","` `modlist -p -s`
ok      example.com/multi/module2       0.115s  coverage: [no statements]
ok      example.com/multi/package1      0.221s  coverage: [no statements]
ok      example.com/multi/module1/package2      0.325s  coverage: [no statements]
ok      example.com/multi       0.429s  coverage: [no statements]
ok      example.com/multi/module1       0.815s  coverage: [no statements]
ok      example.com/multi/module2/internal/pkg  0.928s  coverage: [no statements]
ok      example.com/multi/package2      1.333s  coverage: [no statements]
ok      example.com/multi/module1/package1      1.446s  coverage: [no statements]