ingress-nginx lua plugins documentation

rootfs/etc/nginx/lua/plugins/hello_world/main.lua

@@ -1,14 +1,10 @@
 local _M = {}
 
 function _M.rewrite()
-  ngx.req.set_header("x-hello-world", "1")
-end
-
-function _M.access()
   local ua = ngx.var.http_user_agent
 
   if ua == "hello" then
-    ngx.exit(403)
+    ngx.req.set_header("x-hello-world", "1")
   end
 end
 

rootfs/etc/nginx/lua/plugins/hello_world/test/main_test.lua

@@ -0,0 +1,25 @@
+_G._TEST = true
+
+local main = require("plugins.hello_world.main")
+
+-- The unit tests are run within a timer phase in a headless Nginx process.
+-- Since `set_header` and `ngx.var.http_` API are disabled in this phase we have to stub it 
+-- to avoid `API disabled in the current context` error.
+
+describe("main", function()
+  describe("rewrite", function()
+    it("sets x-hello-world header to 1 when user agent is hello", function()
+      ngx.var = { http_user_agent = "hello" }
+      stub(ngx.req, "set_header")
+      main.rewrite()
+      assert.stub(ngx.req.set_header).was_called_with("x-hello-world", "1")
+    end)
+
+    it("does not set x-hello-world header to 1 when user agent is not hello", function()
+      ngx.var = { http_user_agent = "not-hello" }
+      stub(ngx.req, "set_header")
+      main.rewrite()
+      assert.stub(ngx.req.set_header).was_not_called_with("x-hello-world", "1")
+    end)
+  end)
+end)