test(runtime/health): cover lua healthchecks

- Add tests for lua healthchecks (failure, success and submodules).
- Reword some of the test naming for improved logs readability.
- Modify render test to accomodate the changes of the health autoload function.
- Add test for :checkhealth completion of Lua healtchecks.

test/functional/fixtures/lua/test_plug/health/init.lua

@@ -0,0 +1,11 @@
+local M = {}
+local health = require("health")
+
+M.check = function()
+  health.report_start("report 1")
+  health.report_ok("everything is fine")
+  health.report_start("report 2")
+  health.report_ok("nothing to see here")
+end
+
+return M

test/functional/fixtures/lua/test_plug/submodule/health.lua

@@ -0,0 +1,11 @@
+local M = {}
+local health = require("health")
+
+M.check = function()
+  health.report_start("report 1")
+  health.report_ok("everything is fine")
+  health.report_start("report 2")
+  health.report_ok("nothing to see here")
+end
+
+return M

test/functional/fixtures/lua/test_plug/submodule_failed/health.lua

@@ -0,0 +1,12 @@
+local M = {}
+local health = require("health")
+
+M.check = function()
+  health.report_start("report 1")
+  health.report_ok("everything is fine")
+  health.report_warn("About to add a number to nil")
+  local a = nil + 2
+  return a
+end
+
+return M