Made subscription a bit more picky about its arguments

lib/Announcements/Subscription.pm

@@ -35,6 +35,9 @@ sub BUILDARGS {
     my $params = $class->SUPER::BUILDARGS(@_);
 
     if (my $oneshot = delete $params->{do_once}) {
+        die "You can use 'do', or you can use 'do_once'. You cannot use both"
+            if $params->{do};
+
         $params->{do} = sub {
             $_[2]->unsubscribe;
             $oneshot->(@_);

t/unsubscribing.t

@@ -2,6 +2,7 @@ use Test::More;
 use strict;
 use warnings;
 use Announcements::Subscription;
+use Test::Fatal;
 
 {
     package PushedButton;
@@ -40,7 +41,7 @@ subtest "Basic unsubscription" => sub {
     is $announcement_count, 1;
 };
 
-subtest "Basic unsubscription" => sub {
+subtest "do_once" => sub {
     my $nuke = PushedButton->new;
     my $announcement_count = 0;
 
@@ -57,6 +58,20 @@ subtest "Basic unsubscription" => sub {
     is $announcement_count, 1;
 };
 
+subtest "Do, or do_once, there is no confusion" => sub {
+    isnt(
+        exception {
+            Announcements::Subscription->new(
+                when => 'PushedButton',
+                do => sub { 'one thing' },
+                do_once => sub { 'or the other' },
+            )
+        },
+        undef,
+        "Two params enter, one param leaves"
+    )
+};
+
 subtest "Double subscription is wrong, m'kay?" => sub {
     my $nuke = PushedButton->new;
     my $announcement_count = 0;