spec/policy: add specs for the maintenance policy

spec/policy/maintenance_mode/maintenance_mode_spec.lua

@@ -0,0 +1,52 @@
+local MaintenancePolicy = require('apicast.policy.maintenance_mode')
+
+describe('Maintenance mode policy', function()
+  describe('.rewrite', function()
+    before_each(function()
+      stub(ngx, 'say')
+      stub(ngx, 'exit')
+    end)
+
+    context('when using the defaults', function()
+      local maintenance_policy = MaintenancePolicy.new()
+
+      it('returns 503', function()
+        maintenance_policy:rewrite()
+
+        assert.stub(ngx.exit).was_called_with(503)
+      end)
+
+      it('returns the default message', function()
+        maintenance_policy:rewrite()
+
+        assert.stub(ngx.say).was_called_with('Service Unavailable - Maintenance')
+      end)
+    end)
+
+    context('when using a custom status code', function()
+      it('returns that status code', function()
+        local custom_code = 555
+        local maintenance_policy = MaintenancePolicy.new(
+            { status = custom_code }
+        )
+
+        maintenance_policy:rewrite()
+
+        assert.stub(ngx.exit).was_called_with(custom_code)
+      end)
+    end)
+
+    context('when using a custom message', function()
+      it('returns that message', function()
+        local custom_msg = 'Some custom message'
+        local maintenance_policy = MaintenancePolicy.new(
+            { message = custom_msg }
+        )
+
+        maintenance_policy:rewrite()
+
+        assert.stub(ngx.say).was_called_with(custom_msg)
+      end)
+    end)
+  end)
+end)