Testing functions through I/O in Haskell

I'm playing codewars to sharpen my Haskell skills, and running into a problem that I haven't had in imperative languages.

Let's say I'm writing a function foo() in javascript, which takes an int, adds two, squares it, subtracts one, and returns the square root of that number.

var foo = function(n) {
  n += 2;
  n = n * n;
  n -= 1;
  n = Math.sqrt(n);
}

I want to check on the state of the data being processed in the function at various points to help me troubleshoot/revise/debug code, so I will insert console.log() statements whenever I want to see where I'm at. For example, am I, in fact, squaring the sum of n+2 correctly halfway through the function? Let's see...

var foo = function(n) {
  n += 2;
  n = n * n;
  console.log("n = " + n);
  n -= 1;
  n = Math.sqrt(n);
}

While this example should be simple enough for a Haskeller to write in one line, if you have a complex function and want to check the state at different points, how do Haskellers do it? Is there a standard practice using the IO() monad? Do they get around it some other way?