OK. Thanks.

What language are you working in?

He meant which programming language, it's javascript, isn't it?

See the expected and actual result in two rows:

Expected:    '1 * 5 = 5\n2 * 5 = 10\n3 * 5 = 15\n4 * 5 = 20\n5 * 5 = 25\n6 * 5 = 30\n7 * 5 = 35\n8 * 5 = 40\n9 * 5 = 45\n10 * 5 = 50', 
instead got: '1 * 5 = 5\n2 * 5 = 10\n3 * 5 = 15\n4 * 5 = 20\n5 * 5 = 25\n6 * 5 = 30\n7 * 5 = 35\n8 * 5 = 40\n9 * 5 = 45\n10 * 5 = 50\n'
                                                                                                                                    ^^

They're not the same.

I'm working in English. I use "return" to display the result. The code is working fine in VSCode in strict mode.

Here is the error message:

STDERR
Unhandled rejection TestError: Expected: '1 * 5 = 5\n2 * 5 = 10\n3 * 5 = 15\n4 * 5 = 20\n5 * 5 = 25\n6 * 5 = 30\n7 * 5 = 35\n8 * 5 = 40\n9 * 5 = 45\n10 * 5 = 50', instead got: '1 * 5 = 5\n2 * 5 = 10\n3 * 5 = 15\n4 * 5 = 20\n5 * 5 = 25\n6 * 5 = 30\n7 * 5 = 35\n8 * 5 = 40\n9 * 5 = 45\n10 * 5 = 50\n'

There's no way we can tell you why without seeing your code. Are you misreading the logs off-by-one? What does the error message say? What language are you working in? Are you returning the value or printing the value?

My code gives the same result as expected but all test were rejected. Why?