It was gettig tedious to add the change tracking logic in all of the
methods. And since there likely will be many more such methods, I have
now extracted that bit into its own function.
As I noted in commit 85b9c2459c I noticed
that the testing of the invalidity of invalid struct "deserialization"
was not sound. That was because if one error was not actually thrown,
the test would still be satisfied by the following error. However, if
only that specific thing was wrong, no error would be thrown and an
invalid struct would be accepted.
Therefore I now changed those tests to also check the exception type and
its message. This means that if an exception is missing, it is
immediately picked up.
I also found out that one exception was actually wrong. I had mistyped
`TypeError` as `TypError`. Funnily enough that still causes an exception
to be thrown at that location, but a `ReferenceError` instead of the
`TypeError`. Such bugs should now be more easily noticable.
