
ZTC makes the following assumptions about its environment:

a) The 'ZopeTestCase' package is installed in the Zope "trunk" inside the
   'Testing' module.

b) none

c) none

d) The somewhat weak assumption is that ZTC can walk up the directory tree from
   'tests', and find a 'Products' directory. This is how INSTANCE_HOME 
   detection works. It regrettably fails on some filesystems when symbolic 
   links are involved (a solution is detailed below, so hang on).


The non-trivial part is that INSTANCE_HOME has two distinct purposes:

    1) INSTANCE_HOME/lib/python must be added to sys.path and 
       INSTANCE_HOME/Products to Products.__path__.

    2) INSTANCE_HOME/custom_zodb.py must be used to set up a ZODB.


ZTC attempts to resolve this by detecting an INSTANCE_HOME but leaving
the actual environment variable untouched

As soon as I allow you to set INSTANCE_HOME yourself, I lose the ability to 
distinguish whether you mean 1) or 2) or both. 

Before ZTC 0.6.2 the code assumed "both" and did the magic ZEO dance. This was
clearly too surprising.

The behaviour has now been changed to 1). 

That way, if your setup does not fit c) or you run into the symbolic link 
problem d), you can solve it by setting INSTANCE_HOME prior to running the 
tests.

ZEO support ("both") is handled separately, through the new environment 
variable ZEO_INSTANCE_HOME.
