That's indeed true. I didn't know that, but tried the following, it works:

# file: MyDir/MyTest.pm
package MyDir::Foo;

sub new{
    my $class = shift;
    my $self = {};
    bless $self, $class;
    return $self;
}

sub foo{
    print "Foo\n";
}

package MyDir::Bar;

sub new{
    my $class = shift;
    my $self = {};
    bless $self, $class;
    return $self;
}

sub bar{
    print "Bar\n";
}

1;
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With test code:

use strict;
use MyDir::MyTest;

my $foo = MyDir::Foo->new();
$foo->foo();

my $bar = MyDir::Bar->new();
$bar->bar();
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Updated. In fact, one can simply name the package as "Foo" and "Bar" instead of "MyDir::Foo" and "MyDir::Bar". In other words, "use" is tied to the directory layout, but not to the contents of the files. Am I too general here?