Minor fixes to test tools

[c42f]

• Avoid crash in heuristic Expr comparisons
• reduce_tree(text) returns text not a tree

[codecov[bot]]

Codecov Report

Merging #262 (1b97299) into main (7445401) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #262   +/-   ##
=======================================
  Coverage   96.41%   96.41%           
=======================================
  Files          15       15           
  Lines        3929     3929           
=======================================
  Hits         3788     3788           
  Misses        141      141