tests: Add a simple systray test.

Compile a random little C program found on stack overflow to make
a systray. The goal is to make the `event.c` tests less flacky.

tests/test-systray.lua

@@ -0,0 +1,90 @@
+local spawn = require("awful.spawn")
+local wibox = require("wibox")
+local beautiful = require("beautiful")
+
+local steps, pid1, pid2, draw_w, st = {}
+
+table.insert(steps, function()
+    screen[1].mywibox:remove()
+
+    local widget = wibox.widget.base.make_widget()
+
+    function widget:fit(_, w, h)
+        return w, h
+    end
+
+    function widget:draw(_, _, width)
+        draw_w = width
+    end
+
+    local wb = wibox {
+        x       = 0,
+        y       = 0,
+        width   = 100,
+        height  = 20,
+        visible = true
+    }
+
+    st = wibox.widget.systray()
+
+    wb.widget = {
+        st,
+        widget,
+        layout = wibox.layout.fixed.horizontal
+    }
+
+    pid1 = spawn("./test-systray")
+
+    return true
+end)
+
+table.insert(steps, function()
+    if draw_w ~= 80 then return end
+
+    pid2 = spawn("./test-systray")
+
+    return true
+end)
+
+table.insert(steps, function()
+    if draw_w ~= 60 then return end
+
+    st.reverse = true
+    st.horizontal = false
+
+    return true
+end)
+
+table.insert(steps, function()
+    st.horizontal = true
+
+    beautiful.systray_icon_spacing = 10
+
+    return true
+end)
+
+
+table.insert(steps, function()
+    if draw_w ~= 50 then return end
+
+    st.base_size = 5
+    return true
+end)
+
+
+table.insert(steps, function()
+    if draw_w ~= 80 then return end
+
+    awesome.kill(pid1, 9)
+    awesome.kill(pid2, 9)
+
+    return true
+end)
+
+
+table.insert(steps, function()
+    if draw_w ~= 100 then return end
+    return true
+end)
+
+require("_runner").run_steps(steps)