tests: Add a template to take screenshots of widgets

tests/examples/wibox/template.lua

@@ -0,0 +1,42 @@
+local file_path, image_path, luacovpath = ...   
+
+-- Set the global shims
+-- luacheck: globals awesome client tag
+awesome = require( "awesome" )
+client  = require( "client"  )
+tag     = require( "tag"     )
+
+-- Force luacheck to be silent about setting those as unused globals
+assert(awesome and client and tag)
+
+local wibox   = require( "wibox"         )
+local surface = require( "gears.surface" )
+
+-- If luacov is available, use it. Else, do nothing.
+pcall(function()
+    require("luacov.runner")(luacovpath)
+end)
+
+-- This is the main widget the tests will use as top level
+local container = wibox.layout.fixed.vertical()
+
+-- Let the test request a size and file format
+local w, h, image_type = loadfile(file_path)(container)
+image_type = image_type or "svg"
+
+-- Emulate the event loop for 10 iterations
+for _ = 1, 10 do
+    awesome:emit_signal("refresh")
+end
+
+-- Get the example fallback size (the tests can return a size if the want)
+local f_w, f_h = container:fit({dpi=96}, 9999, 9999)
+
+-- There is an overhead that cause testbox "...", add 10 until someone
+-- figures out the real equation
+f_w, f_h = f_w+10, f_h+10
+
+-- Save to the output file
+local img = surface["widget_to_"..image_type](container, image_path.."."..image_type, w or f_w, h or f_h)
+img:finish()
+