I removed all tests where expected and actual values were switched. But there are still tests in the form

let k = global.expected;
assert.strictEqual(next(), k, "Modify expected variable");

Yes, there are also test cases in the form strictEqual(expected, next()).

The No modify expected variable test looks like this:

let k = global.expected;
assert.strictEqual(next(), k, "Modify expected variable");

Hint: you need to do something outside of the function next in order to pass this test. (The initial solution has this line: // Hint: Initial code.)

Please post your current solution in a comment with the spoiler flag.

How come?

I've been trying to solve it for one hour and still can't find the solution...

Do you have enough thumb down?

Yep, sorry for any lack of clarity. JS cannot replace an arbitrary function reference (e.g. function (someFunc) { ... } cannot "swap out" someFunc, except as a locally-scoped binding). It can replace a variable or property name referring to a function (e.g. function(obj, methodName) { ... } CAN substitute a new value into object[methodName]). That latter can be used in a hacky way to replace top-level variables: replaceMethod(global, 'funcName') could reassign global[funcName].