tablex: Skip equality comparison in equal fn

The second loop doesn't care if the values are equal. It only checks if
the keys are there. The first loop already checked for equality.

Add tests to prove correctness using testy.lua.

tablex.lua

@@ -417,8 +417,9 @@ function tablex.shallow_equal(a, b)
 			return false
 		end
 	end
+	-- second loop to ensure a isn't missing any keys from b.
 	for k, v in pairs(b) do
-		if a[k] ~= v then
+		if a[k] == nil then
 			return false
 		end
 	end
@@ -442,8 +443,10 @@ function tablex.deep_equal(a, b)
 			return false
 		end
 	end
+	-- second loop to ensure a isn't missing any keys from b, so we can skip
+	-- recursion.
 	for k, v in pairs(b) do
-		if not tablex.deep_equal(v, a[k]) then
+		if a[k] == nil then
 			return false
 		end
 	end

tests.lua

@@ -0,0 +1,45 @@
+-- Run this file with testy:
+--	  testy.lua tests.lua
+-- testy sets `...` to "module.test", so ignore that and use module top-level paths.
+package.path = package.path .. ";../?.lua"
+
+local assert = require("batteries.assert")
+local tablex = require("batteries.tablex")
+
+
+-- tablex {{{
+
+local function test_shallow_equal()
+	local x,y
+	x = { a = { b = { 2 }, } }
+	y = { a = { b = { 2 }, } }
+	assert(not tablex.shallow_equal(x, y))
+
+	x = { 3, 4, "hello", [20] = "end", }
+	y = { 3, 4, "hello", [20] = "end", }
+	assert(tablex.shallow_equal(x, y))
+
+	local z = { 1, 2, }
+	x = { a = z, b = 10, c = true, }
+	y = { a = z, b = 10, c = true, }
+	assert(tablex.shallow_equal(x, y))
+	assert(tablex.shallow_equal(y, x))
+end
+
+local function test_deep_equal()
+	local x,y
+	x = { a = { b = { 2 }, c = { 3 }, } }
+	y = { a = { b = { 2 }, c = { 3 }, } }
+	assert(tablex.deep_equal(x, y))
+
+	x = { a = { b = { 1, 2 }, c = { 3 }, } }
+	y = { a = { c = { 3 }, b = { [2] = 2, [1] = 1 }, } }
+	assert(tablex.deep_equal(x, y))
+	assert(tablex.deep_equal(y, x))
+
+	x = { a = { b = { 2 }, c = { 3 }, 2 } }
+	y = { a = { b = { 2 }, c = { 3 }, } }
+	assert(not tablex.deep_equal(x, y))
+	assert(not tablex.deep_equal(y, x))
+end
+