Adapt luassert failure messages to luanit to avoid luaunit interpreting them as errors

luassert_luaunit_adapter.lua

-- execute dofile("luassert_luaunit_adapter.lua")
-- then execute dofile("file_with_your_tests.lua"

local luaunit = require("luaunit")
local astate = require("luassert.state")
local util = require("luassert.util")

---prepends LuaUnit FAILURE_PREFIX to luassert custom failure message
---in order to make LuaUnit pick up test failures as failures instead of errors.
local function prepender(state, arguments, level)
	local failure_message = rawget(state, "failure_message")
	if util.hastostring(failure_message) then
		failure_message = luaunit.FAILURE_PREFIX .. tostring(failure_message)
	  elseif failure_message ~= nil then
		failure_message = luaunit.FAILURE_PREFIX .. astate.format_argument(failure_message)
	else
		failure_message = luaunit.FAILURE_PREFIX
	end
	state.failure_message = failure_message
end

---patch assert.register function to register modifier
---for assertions which get registered later.
local assert = require("luassert.assert")
local org_register = rawget(assert, "register")
assert.register = function(self, nspace, name, callback, positive_message, negative_message)
	if nspace == "assertion" then
		org_register(self, "modifier", name, prepender)
	end
	org_register(self, nspace, name, callback, positive_message, negative_message)
end

---register modifier for already registered assertions
---(e.g. in case luassert.assertions was already loaded)
local namespace = require("luassert.namespaces")
for k, _ in pairs(namespace.assertion or {}) do
	assert:register("modifier", k, prepender)
end