You only need to mock the members of the SOAP::Lite interface that you are actually using. Consider:

use strict;
use warnings;
use Test::MockObject;
use Test::More;

my $mockSOAP = Test::MockObject->new();

$mockSOAP->fake_module('SOAP::Lite', new => sub {SOAP_new ($mockSOAP, 
+@_)},);
$mockSOAP->mock(soapversion => \&SOAP_soapversion);

use_ok('SOAP::Lite');


my $client = SOAP::Lite->new(proxy => 'blah');

is($client->soapversion(), 1.2, 'Version ok');

eval {$client->soapversion(1.3)};
my $result = $@;

is($result, "Can't set SOAP version to 1.3\n", 'Bad version rejected')
+;
done_testing();


sub SOAP_new {
    my ($mock, $class, %params) = @_;
    
    $params{version} ||= 1.2;
    $mock->{newParams} = \%params;
    $mock->{newClass} = $class;
    return $mock;
}


sub SOAP_soapversion {
    my ($self, $version) = @_;

    die "Can't set SOAP version to $version\n"
        if defined $version && $version != 1.2 && $version != 1.1;

    $self->{newParams}{version} = $version if defined $version;
    return $self->{newParams}{version};
}
[download]

Prints:

ok 1 - use SOAP::Lite;
ok 2 - Version ok
ok 3 - Bad version rejected
1..3
[download]