There should also be fixed and random test cases of bracket mis-swapped, like ][ and []1, 2, 3][

should have fixed tests like [[1, 2] [3, 4]] ---> null, but the reference solution would not handle it

For simplicity, only number literals appear in the array

• Hexadecimal literals with lowercase letters are not tested
• Octal literals are not tested
• Binary literals are not tested (these are not supported by all languages but I'll mention it anyway)
• Floats are not tested

Considering how weak the tests are in this regard, IMO it'd be easier to get rid of this specification and use decimal integers only.

No random tests with hexadecimals and decimals in scientific notation.

Math markup could be used to present formulas.

Would it make sense to include invalid test cases such as "[4 2]" or "[abc]"? Or are such cases ruled out by the fact that the content of the array is supposed to be limited to number literals?

• Your input contains multiple roots easily (they're just polynomials after all); in fact the second one already has 2 roots. Which one should we return?
• What is the range of r?
• NaN is expected if numbers of only one sign appears in the input, but it's not specified at all
• Your second test case is just flat out wrong: The root is not 2.371925354, but 2.371924299
• As mentioned below, test feedback is awful
• And you flipped the expected and actual arguments too
• No random tests

Looks like you're trying to make a polynomial root finding kata without understanding much about polynomials at all. Perhaps you should try again in another kata ;-)

No test cases.
Message: "True should equal False" does not provide any useful feedback.