add better error when object config incomplete

When a service config is missing "value" or "config", it must be an
object. If it is then also missing a "class", we get a cryptic error:
"argument is not a module name". This is coming from Module::Runtime
use_module.

Now, if this situation happens, we throw an exception with a better
error message.

lib/Beam/Wire.pm

@@ -478,6 +478,14 @@ sub create_service {
         return $self->_load_config( "$conf_path" );
     }
 
+    if ( !$service_info{class} ) {
+        Beam::Wire::Exception::InvalidConfig->throw(
+            name => $name,
+            file => $self->file,
+            error => 'Service configuration incomplete. Missing one of "class", "value", "config"',
+        );
+    }
+
     use_module( $service_info{class} );
 
     if ( my $with = $service_info{with} ) {

t/method/create_service.t

@@ -0,0 +1,40 @@
+
+use strict;
+use warnings;
+use Test::More;
+use Test::Lib;
+use Test::Deep;
+use Test::Exception;
+use Beam::Wire;
+
+my $wire = Beam::Wire->new(
+    config => {
+        base_class => {
+            class => 'My::ArgsTest',
+        },
+        base_no_class => { },
+    },
+);
+
+my $svc;
+
+lives_ok { $svc = $wire->create_service( 'testing', class => 'My::ArgsTest' ) }
+    'create service with class only';
+cmp_deeply $svc->got_args, [], 'no args given';
+
+throws_ok { $svc = $wire->create_service( 'testing', path => '/foo/bar' ) }
+    'Beam::Wire::Exception::InvalidConfig',
+    'must have one of "class", "value", "config" in the merged config';
+
+throws_ok { $svc = $wire->create_service( 'testing', extends => 'base_no_class' ) }
+    'Beam::Wire::Exception::InvalidConfig',
+    'merged config from extends must have one of "class", "value", "config" in the merged config';
+
+throws_ok { $svc = $wire->create_service( 'testing', class => 'My::ArgsTest', value => '' ) }
+    'Beam::Wire::Exception::InvalidConfig',
+    'cannot use "value" with "class"';
+throws_ok { $svc = $wire->create_service( 'testing', extends => 'base_class', value => '' ) }
+    'Beam::Wire::Exception::InvalidConfig',
+    'cannot use "value" with "extends"';
+
+done_testing;