Here is a function that can test form submission trigger functions, lifted from How can I test a trigger function in GAS?.
function test_onFormSubmit() {
var dataRange = SpreadsheetApp.getActiveSheet().getDataRange()
var data = dataRange.getValues();
var headers = data[0];
// Start at row 1, skipping headers in row 0
for (var row=1; row < data.length; row++) {
var e = {};
e.values = data[row];
e.range = dataRange.offset(row,0,1,data[0].length);
e.namedValues = {};
// Loop through headers to create namedValues object
for (var col=0; col<headers.length; col++) {
e.namedValues[headers[col]] = e.values[col];
}
// Pass the simulated event to onFormSubmit
onFormSubmit(e);
}
}