A pattern to debug google apps script (GAS) triggered functions.

GAS-Trigger-TestingFunction.gs

/**
 * Test function for onEdit. Passes an event object to simulate an edit to
 * a cell in a spreadsheet.
 *
 * Check for updates: http://stackoverflow.com/a/16089067/1677912
 *
 * See https://developers.google.com/apps-script/guides/triggers/events#google_sheets_events
 * 
 * on Script editor, set to debug THIS function, but create breakpoints
 * on the onEdit Function
 */
function test_onEdit() {
  onEdit({
    user : Session.getActiveUser().getEmail(),
    source : SpreadsheetApp.getActiveSpreadsheet(),
    range : SpreadsheetApp.getActiveSpreadsheet().getActiveCell(),
    value : SpreadsheetApp.getActiveSpreadsheet().getActiveCell().getValue(),
    authMode : "LIMITED"
  });
}