A memory leak occurs when a Perl data structure is destroyed but some of
the contents of that structure are not freed. Leaked memory is a useless
overhead. Leaks can significantly impact system performance. They can also
cause an application to abend due to lack of memory.

In Perl, circular references are a common cause of memory leaks. Circular
references are allowed in Perl, but data structures containing circular
references will leak memory unless the programmer takes specific measures
to prevent leaks. Preventive measures include weakening the references
and arranging to break the reference cycle just before the structure is
destroyed.

When using circular references, it is easy to misdesign or misimplement a
scheme for preventing memory leaks. Mistakes of this kind have been hard to
detect in a test suite.

Test::Weaken allows easy detection of unfreed Perl data. Test::Weaken allows
you to examine the unfreed data, even data that would usually have been made
inaccessible.

Test::Weaken frees the test structure, then looks to see if any of the
contents of the structure were not actually deallocated. By default,
Test::Weaken determines the contents of a data structure by examining
arrays and hashes, by following references, and by following tied variables
to their underlying object. Test::Weaken does this recursively to unlimited
depth.

Test::Weaken can deal with circular references without going into infinite
loops. Test::Weaken will not visit the same Perl data object twice.