msg:
{ actual, expected, asString ? false, asJSON ? false, removeDunders ? false, }:
let
  preProcess = v: 
  if removeDunders then
    builtins.removeAttrs v [ "__toString" "__functor" ]
  else if asString then
    toString v
  else if asJSON then
    builtins.toJSON v
  else v;
  
  a = preProcess actual;
  e = preProcess expected;

in
if (a == e) then ''
    echo 'it ${msg}'
  ''
else
  ''
    echo 'FAILED: ${msg}'
    echo '${builtins.toJSON expected}'
    echo '${builtins.toJSON actual}'
  ''