fix: use ipairs in functional.all and add basic test coverage

lua/plenary/functional.lua

@@ -40,15 +40,14 @@ function f.any(fun, iterable)
 end
 
 function f.all(fun, iterable)
-  for k, v in pairs(iterable) do
+  for k, v in ipairs(iterable) do
     if not fun(k, v) then
       return false
     end
   end
 
   return true
 end
-
 function f.if_nil(val, was_nil, was_not_nil)
   if val == nil then
     return was_nil

tests/plenary/functional_spec.lua

@@ -15,4 +15,44 @@ describe("functional", function()
       assert.is.equal(expected, f.partial(args, 1, 2, 3, 4)())
     end)
   end)
-end)
+
+    describe("all", function()
+      it("returns true when all elements satisfy predicate", function()
+        assert.is_true(f.all(function(_, x) return x < 10 end, {1, 2, 3, 4}))
+      end)
+
+      it("returns false if any element fails predicate", function()
+        assert.is_false(f.all(function(_, x) return x < 10 end, {1, 2, 30, 4}))
+      end)
+
+      it("returns true on empty list", function()
+        assert.is_true(f.all(function(_, x) return false end, {}))
+      end)
+    end)
+
+    describe("any", function()
+      it("returns true if any element satisfies predicate", function()
+        assert.is_true(f.any(function(_, v) return v > 10 end, {1, 2, 12, 4}))
+      end)
+
+      it("returns false when no elements match", function()
+        assert.is_false(f.any(function(_, v) return v > 10 end, {1, 2, 3, 4}))
+      end)
+
+      it("returns false on empty list", function()
+        assert.is_false(f.any(function(_, v) return true end, {}))
+      end)
+    end)
+
+    describe("if_nil", function()
+      it("returns was_nil value if nil", function()
+        assert.equals("fallback", f.if_nil(nil, "fallback", "not nil"))
+      end)
+
+      it("returns was_not_nil value if not nil", function()
+        assert.equals("not nil", f.if_nil(5, "fallback", "not nil"))
+      end)
+    end)
+  end)
+
+