Update InputSender documentation for "emit" approach.

[bitwes]

          I think you could put these informations in the [DOCS](https://gut.readthedocs.io/en/latest/Mocking-Input.html).

It would help a lot beginners, I was searching these information for three days already.

Thank you you put here!

Information 1

There is some stuff in the InputSender that makes this a little cleaner, but the "waits" are necessary. You can string all your commands together and there is wait_frames and wait_secs built into the sender. There's also hold_for which can save you a "button up". You can then wait for the idle signal on the sender.

Some waits can be skipped in different scenarios (such as no wait between your button down/up). But if you want something like just_pressed you have to use waits (I'm pretty sure).

Here's another way to write that test without using any direct calls to wait_frames.

func test_open_settings_menu() -> void:
	var settings_button_pos = button_settings.get_global_position()
	_sender.mouse_set_position(settings_button_pos, settings_button_pos)\
		.wait_frames(1)\
		.mouse_left_button_down(settings_button_pos, settings_button_pos)\
		.hold_for('1f')\ # holds the button down for one frame, for illustration purposes, no button up needed
		.wait_frames(1)
	await _sender.idle

	assert_eq(main_menu.visible,false)
	assert_eq(settings_menu.visible,true)

Information 2

I absolutely love seeing people using InputSender, but if you are only checking that you are handling the button pressed correctly then the following is a better test.

func test_open_settings_menu_seconds() -> void:
	button_settings.pressed.emit()
	assert_eq(main_menu.visible, false)
	assert_eq(settings_menu.visible, true)

If all of your buttons are standard buttons then it is overkill to test whether or not they work with the mouse (a minor case of "testing the framework"). Getting a reference to

I believe the second information is more simple to use, and draw attention that also exists button_up and button_down could help more people.

Originally posted by @hugarty in #511 (comment)