refactor balancer into more testable and extensible interface

rootfs/etc/nginx/lua/test/balancer/chash_test.lua

@@ -1,6 +1,31 @@
-local cwd = io.popen("pwd"):read('*l')
-package.path = cwd .. "/rootfs/etc/nginx/lua/?.lua;" .. package.path
+package.path = "./rootfs/etc/nginx/lua/?.lua;./rootfs/etc/nginx/lua/test/mocks/?.lua;" .. package.path
 
-describe("[chash_test]", function()
-  -- TODO(elvinefendi) add unit tests
+describe("Balancer chash", function()
+  local balancer_chash = require("balancer.chash")
+
+  describe("balance()", function()
+    it("uses correct key for given backend", function()
+      _G.ngx = { var = { request_uri = "/alma/armud" }}
+
+      local resty_chash = package.loaded["resty.chash"]
+      resty_chash.new = function(self, nodes)
+        return {
+          find = function(self, key)
+            assert.equal("/alma/armud", key)
+            return "10.184.7.40:8080"
+          end
+        }
+      end
+
+      local backend = {
+        name = "my-dummy-backend", ["upstream-hash-by"] = "$request_uri",
+        endpoints = { { address = "10.184.7.40", port = "8080", maxFails = 0, failTimeout = 0 } }
+      }
+      local instance = balancer_chash:new(backend)
+
+      local host, port = instance:balance()
+      assert.equal("10.184.7.40", host)
+      assert.equal("8080", port)
+    end)
+  end)
 end)