A developer has a fizzbuzz function that, when passed in a number, returns the following:'...

The correct answers are B and D .

A strong test case checks whether the actual output matches the expected behavior of the function.

For Option B :

let res = fizzbuzz(15);

console.assert(res === ' fizzbuzz ' );

The number 15 is divisible by both 3 and 5:

15 % 3 === 0

15 % 5 === 0

So the correct return value is:

' fizzbuzz '

That makes option B a valid test.

For Option D :

let res = fizzbuzz(Infinity);

console.assert(res === ' ' );

Infinity is not a normal finite divisible number. In JavaScript:

Infinity % 3

Infinity % 5

produce NaN, and comparisons such as:

Infinity % 3 === 0

are false.

So a typical fizzbuzz implementation would not treat Infinity as divisible by 3 or 5, meaning it should return:

' '

That makes option D a valid test for the “neither divisible by 3 nor 5” path.

Now compare the incorrect options:

Option A is wrong because:

fizzbuzz(3)

should return:

' fizz '

not:

' buzz '

Option C is wrong because the function specification says the function returns strings such as ' fizz ' , ' buzz ' , ' fizzbuzz ' , or ' ' . It does not say the function returns numeric NaN.

So this assertion is not appropriate:

console.assert(isNaN(res));

Therefore, the verified answers are B and D .