add coverage.py module to tests directory.
written by ned batchelder and gareth rees.
%% no merges expected
%% merge should fail
abort: 'b' already exists in the working dir and differs from remote
%% merge of b expected
merging for b
merging b
%%
Contents of b should be "this is file b1"
This is file b1
%% merge fails
abort: outstanding uncommitted changes
%% merge expected!
merging for b
merging b
%% merge of b should fail
abort: outstanding uncommitted changes
%% merge of b expected
merging for b
merging b