The comment of the method says the following:

String >> #asInteger
    "Return the integer present in the receiver, or nil. In case of float, returns the integer part."
    ....

But is not clear. Does returns the integer represented by String, what happens if the String is not an integer.

As an example, let's look at this:

'Weird222String' asInteger. "222"
'Weird222String111' asInteger. "222"
'333Weird222String111' asInteger. "333"

If we see into the implementation, the method returns the first characters that can be parsed as an integer and it stops as soon as there is something else.

I propose to use the NumberParser to parse the String and raise an exception if the complete String does not correspond to an integer.