res.locals not passed to pug template during tests

I'm making an app using Express and using Pug as the templating engine.

In my app.js file, I set a local variable like this: res.locals.user = req.user

Now, this local variable is available to all my views and I'm able to use user and it appears correctly when I run the app.

The problem happens when I try to run integration tests on my app. I always get a TypeError for all res.locals variables:

TypeError: /Users/dakshshah/Documents/Work/Git-Works/getfit/views/layout.pug:4
    2| html
    3|   head
  > 4|     title= `${title} | ${h.siteName}`
    5|     link(rel='stylesheet', href='/dist/style.css')
    6|     link(rel="shortcut icon" type="image/png" href="/images/icons/favicon.png")
    7|     meta(name="viewport" content="width=device-width, initial-scale=1")

Cannot read property 'siteName' of undefined

.... error stack ....

Why are the res.locals variables not being passed to Pug during tests but work perfectly fine when using the app?