util.hashring: Add tests

spec/util_hashring_spec.lua

@@ -0,0 +1,85 @@
+local hashring = require "util.hashring";
+
+describe("util.hashring", function ()
+
+	local sha256 = require "util.hashes".sha256;
+
+	local ring = hashring.new(128, sha256);
+
+	it("should fail to get a node that does not exist", function ()
+		assert.is_nil(ring:get_node("foo"))
+	end);
+
+	it("should support adding nodes", function ()
+		ring:add_node("node1");
+	end);
+
+	it("should return a single node for all keys if only one node exists", function ()
+		for i = 1, 100 do
+			assert.is_equal("node1", ring:get_node(tostring(i)))
+		end
+	end);
+
+	it("should support adding a second node", function ()
+		ring:add_node("node2");
+	end);
+
+	it("should fail to remove a non-existent node", function ()
+		assert.is_falsy(ring:remove_node("node3"));
+	end);
+
+	it("should succeed to remove a node", function ()
+		assert.is_truthy(ring:remove_node("node1"));
+	end);
+
+	it("should return the only node for all keys", function ()
+		for i = 1, 100 do
+			assert.is_equal("node2", ring:get_node(tostring(i)))
+		end
+	end);
+
+	it("should support adding multiple nodes", function ()
+		ring:add_nodes({ "node1", "node3", "node4", "node5" });
+	end);
+
+	it("should disrupt a minimal number of keys on node removal", function ()
+		local orig_ring = ring:clone();
+		local node_tallies = {};
+
+		local n = 1000;
+
+		for i = 1, n do
+			local key = tostring(i);
+			local node = ring:get_node(key);
+			node_tallies[node] = (node_tallies[node] or 0) + 1;
+		end
+
+		--[[
+		for node, key_count in pairs(node_tallies) do
+			print(node, key_count, ("%.2f%%"):format((key_count/n)*100));
+		end
+		]]
+
+		ring:remove_node("node5");
+
+		local disrupted_keys = 0;
+		for i = 1, n do
+			local key = tostring(i);
+			if orig_ring:get_node(key) ~= ring:get_node(key) then
+				disrupted_keys = disrupted_keys + 1;
+			end
+		end
+		assert.is_equal(node_tallies["node5"], disrupted_keys);
+	end);
+
+	it("should support removing multiple nodes", function ()
+		ring:remove_nodes({"node2", "node3", "node4", "node5"});
+	end);
+
+	it("should return a single node for all keys if only one node remains", function ()
+		for i = 1, 100 do
+			assert.is_equal("node1", ring:get_node(tostring(i)))
+		end
+	end);
+
+end);