Added some tests to ensure that failures work as expected

Also moved the ok() docs first and started filling them out.

lib/Test/XPath.pm

@@ -209,6 +209,22 @@ L<XML::LibXML::Parser options|XML::LibXML::Parser/"PARSER OPTIONS">, such as
 
 =back
 
+=head3 ok
+
+  $xp->ok( '//foo/bar', 'Should have bar element under foo element' );
+  $xp->ok('/contains(//title, "Welcome")', 'Title should contain "Welcome"');
+
+Test that an XPath expression evaluated against the XML document returns a
+true value. If the XPath expression finds no nodes, the result will be false.
+If it finds a value, the value must be a true value (in the Perl sense).
+
+  $xp->ok('//assets/story', sub {
+      my $i;
+      for my $story (@_) {
+          $story->is('[@id]/text()', ++$i, "ID should be $i in story" );
+      }
+  }, 'Should have story elements' );
+
 =head3 is
 
   $xp->is('/html/head/title', 'Welcome');
@@ -229,16 +245,6 @@ L<XML::LibXML::Parser options|XML::LibXML::Parser/"PARSER OPTIONS">, such as
 
   $xp->cmp_ok()
 
-=head3 ok
-
-  $xp->ok( '//foo/bar', 'Should have bar element under foo element' );
-  $xp->ok( '//assets/story', sub {
-      my $i;
-      for my $story (@_) {
-          $story->is('[@id]/text()', ++$i, "ID should be $i in story" );
-      }
-  }, 'Should have story elements' );
-
 =head1 Support
 
 This module is stored in an open GitHub repository,

t/simple.t

@@ -1,7 +1,7 @@
 #!/usr/bin/perl -w
 
 use strict;
-use Test::Builder::Tester tests => 15;
+use Test::Builder::Tester tests => 21;
 use Test::More;
 
 BEGIN { use_ok 'Test::XPath' or die; }
@@ -44,19 +44,59 @@ $xp->like( '/html/head/title', qr{^Hel{2}o$}, 'like should work');
 $xp->unlike( '/html/head/title', qr{^Bye$}, 'unlike should work');
 $xp->cmp_ok('/html/head/title', 'eq', 'Hello', 'cmp_ok should work');
 
+# Make them fail.
+test_out('not ok 1 - is should work');
+test_out('not ok 2 - isnt should work');
+test_out('not ok 3 - like should work');
+test_out('not ok 4 - unlike should work');
+test_out('not ok 5 - cmp_ok should work');
+$xp->is( '/html/head/title', 'Bye', 'is should work');
+$xp->isnt( '/html/head/title', 'Hello', 'isnt should work');
+$xp->like( '/html/head/title', qr{^Bye$}, 'like should work');
+$xp->unlike( '/html/head/title', qr{^Hel{2}o$}, 'unlike should work');
+$xp->cmp_ok('/html/head/title', 'ne', 'Hello', 'cmp_ok should work');
+test_test(
+    skip_err => 1,
+    title => 'Failures in the simple methods should work',
+);
+
 # Try multiples.
 $xp->is('/html/body/p', 'firstpost', 'Should work for multiples');
 
 # Try an attribute.
 $xp->is('/html/body/p/@class', 'foo', 'Should get attribute value');
+$xp->ok('/html/body/p[@class="foo"]', 'Should find by attribute value');
 
 # Try a function.
 $xp->is('count(/html/body/p)', 2, 'Should work for functions');
 
-# Try a boolean function.
-$xp->ok('boolean(1)', 'Boolean should work');
+# Try boolean function.
+$xp->ok('boolean(1)', 'boolean(1) should be true');
+$xp->ok('true()', 'true() should be true');
 
 # Try a false boolean.
 test_out('not ok 1 - false boolean');
 $xp->ok('false()', 'false boolean');
-test_test( skip_err => 1 );
+test_test(
+    skip_err => 1,
+    title => 'Boolean true returned by XPath should be true in ok()',
+);
+
+# Try a comparison function.
+$xp->ok('contains(//title, "Hell")', 'Title should contain "hell"');
+
+# Try a false comparison.
+test_out('not ok 1 - heck');
+$xp->ok('contains(//title, "Heck")', 'heck');
+test_test(
+    skip_err => 1,
+    title => 'Boolean false returned by XPath should be false in ok()',
+);
+
+# Try a non-existent node.
+test_out('not ok 1');
+$xp->ok('/foo/baz');
+test_test(
+    skip_err => 1,
+    title => 'Nonexistent node should be false in ok()',
+);