util.poll: Expand stub tests

Because tests good.

spec/util_poll_spec.lua

@@ -1,6 +1,35 @@
-describe("util.poll", function ()
-	it("loads", function ()
-		require "util.poll"
+describe("util.poll", function()
+	local poll;
+	setup(function()
+		poll = require "util.poll";
 	end);
+	it("loads", function()
+		assert.is_table(poll);
+		assert.is_function(poll.new);
+		assert.is_string(poll.api);
+	end);
+	describe("new", function()
+		local p;
+		setup(function()
+			p = poll.new();
+		end)
+		it("times out", function ()
+			local fd, err = p:wait(0);
+			assert.falsy(fd);
+			assert.equal("timeout", err);
+		end);
+		it("works", function()
+			-- stdout should be writable, right?
+			assert.truthy(p:add(1, false, true));
+			local fd, r, w = p:wait(1);
+			assert.is_number(fd);
+			assert.is_boolean(r);
+			assert.is_boolean(w);
+			assert.equal(1, fd);
+			assert.falsy(r);
+			assert.truthy(w);
+			assert.truthy(p:del(1));
+		end);
+	end)
 end);