Add error handling tests to procrustes
Add tests for handle_error_codes with no error
increase parse_fastq coverage
increase coverage of record_finder
Add data files for OrdinationResults.from_file

To test error handling
Add test for GeneticCode.__eq__ with type mismatch
Add tests for pre_and_postorder with no children
Add test for TreeNode.create_caches with duplicate tips
Add test for empty tree in TreeNode.from_newick
Add AttributeError checks

necessary for py3
Add tests for TreeNode.to_newick for single-node trees

Also simplify logic a bit in TreeNode.to_newick
Add tests for TreeNode.to_newick with >1 node
Add tests for error handling in TreeNode.tip_tip_distances
Add tests for TreeNode.compare_tip_distances
Add tests for error handling in cmdline_generator
Add test for SequenceCollection.toFasta
Add tests for Alignment.subalignment with everything filtered out
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Add tests for Alignment.to_phylip error handling
Add error-handling tests for distribution plotting code