This test does the following:
-Makes a call to pushState()
-Makes sure the history length is correct
-Makes a call to replaceState()
-Makes sure the history length is correct
-Goes back, and makes sure the popstate event is correct
-Goes forward, and makes sure the popstate event represents the replaced state object

History length is 2
History length is 2
State popped - null (type object)
State popped - 1 (type number)