gistfile1.p6

# file Base.pm6
use v6;
unit module Base;
use Base::Test;

# file Base/Test.pm6
use v6;
unit module Base;

our sub foo { say "foo"; }

# repl
> use Base;
> Base::foo;
Could not find symbol '&foo'

Those are two separate modules with the same name.

Perl 6 does not have the same simple namespace that Perl 5 has.

Example/A.pm6

unit module Example;
sub foo () { say 'Alpha' }

Example/B.pm6

unit module Example;
sub foo () { say 'Beta' }

{
  use Example::A;
  Example::foo();
}
{
  use Example::B;
  Example::foo();
}

That prints:

Alpha
Beta

---

You can do the following though:

Base.pm6

use v6;
unit module Base;
use Base::Test;

our &foo = &Base::Test::foo;

Base/Test.pm6

use v6;
unit module Base::Test;

our sub foo { say "foo"; }

REPL

> use Base;
> Base::foo;
foo