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

Copy handler: 
Legacy
DataTransferItemList
Paste handler: 
Legacy
DataTransferItemList

Tests copy / paste and DataTransferItemList

On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".

Running test with Legacy copy handler and Legacy paste handler
PASS testDataTransfer.getData("custom-data") is "hello world"
PASS testDataTransfer.clearData(nonConvertibleToString) threw exception Exception in toString().
PASS testDataTransfer.getData("custom-data") is "hello world"
PASS testDataTransfer.types.length is 4
PASS testDataTransfer.types.indexOf("text/plain") >= 0 is true
PASS testDataTransfer.types.indexOf("text/uri-list") >= 0 is true
PASS testDataTransfer.types.indexOf("text/html") >= 0 is true
PASS testDataTransfer.types.indexOf("custom-data") >= 0 is true
PASS testDataTransfer.getData("text") is "sample"
PASS testDataTransfer.getData("url") is "http://www.google.com/"
PASS testDataTransfer.getData("text/html") is "<em>Markup</em>"
PASS testDataTransfer.getData("custom-data") is "hello world"
Running test with Legacy copy handler and DataTransferItemList paste handler
PASS testDataTransfer.getData("custom-data") is "hello world"
PASS testDataTransfer.clearData(nonConvertibleToString) threw exception Exception in toString().
PASS testDataTransfer.getData("custom-data") is "hello world"
PASS testDataTransfer.items.length is 4
PASS JSON.stringify(expectedTypes) is JSON.stringify(types)
PASS testData is expectedTestData
PASS testData is expectedTestData
PASS testData is expectedTestData
PASS testData is expectedTestData
Running test with DataTransferItemList copy handler and Legacy paste handler
PASS testDataTransfer.items.item is undefined.
PASS testDataTransfer.types.length is 4
PASS testDataTransfer.types.indexOf("text/plain") >= 0 is true
PASS testDataTransfer.types.indexOf("text/uri-list") >= 0 is true
PASS testDataTransfer.types.indexOf("text/html") >= 0 is true
PASS testDataTransfer.types.indexOf("custom-data") >= 0 is true
PASS testDataTransfer.getData("text") is "sample"
PASS testDataTransfer.getData("url") is "http://www.google.com/"
PASS testDataTransfer.getData("text/html") is "<em>Markup</em>"
PASS testDataTransfer.getData("custom-data") is "hello world"
Running test with DataTransferItemList copy handler and DataTransferItemList paste handler
PASS testDataTransfer.items.item is undefined.
PASS testDataTransfer.items.length is 4
PASS JSON.stringify(expectedTypes) is JSON.stringify(types)
PASS testData is expectedTestData
PASS testData is expectedTestData
PASS testData is expectedTestData
PASS testData is expectedTestData
PASS successfullyParsed is true

TEST COMPLETE