To manually test, press your browser shortcut for copy and then for paste. Several lines that say 'PASS' should appear below.

Copy handler: 
Paste handler: 
Running test with Legacy copy handler and Legacy paste handler
PASS: 4 === 4
PASS: sample === sample
PASS: http://www.google.com/ === http://www.google.com/
PASS: <em>Markup</em> === <em>Markup</em>
PASS: hello world === hello world
Running test with Legacy copy handler and DataTransferItemList paste handler
PASS: 4 === 4
PASS: [{"kind":"string","type":"custom-data"},{"kind":"string","type":"text/html"},{"kind":"string","type":"text/plain"},{"kind":"string","type":"text/uri-list"}] === [{"kind":"string","type":"custom-data"},{"kind":"string","type":"text/html"},{"kind":"string","type":"text/plain"},{"kind":"string","type":"text/uri-list"}]
PASS: hello world === hello world
PASS: <em>Markup</em> === <em>Markup</em>
PASS: sample === sample
PASS: http://www.google.com/ === http://www.google.com/
Running test with DataTransferItemList copy handler and Legacy paste handler
PASS: 4 === 4
PASS: sample === sample
PASS: http://www.google.com/ === http://www.google.com/
PASS: <em>Markup</em> === <em>Markup</em>
PASS: hello world === hello world
Running test with DataTransferItemList copy handler and DataTransferItemList paste handler
PASS: 4 === 4
PASS: [{"kind":"string","type":"custom-data"},{"kind":"string","type":"text/html"},{"kind":"string","type":"text/plain"},{"kind":"string","type":"text/uri-list"}] === [{"kind":"string","type":"custom-data"},{"kind":"string","type":"text/html"},{"kind":"string","type":"text/plain"},{"kind":"string","type":"text/uri-list"}]
PASS: hello world === hello world
PASS: <em>Markup</em> === <em>Markup</em>
PASS: sample === sample
PASS: http://www.google.com/ === http://www.google.com/