It turns out my guess was wrong. Ariba is only built to support the default python3 version which makes reliability tough during transitions. The attached patch builds for all version, which should solve any remaining test issues.
Since this has been sitting around for quite some time and it is a transition blocker I intend to NMU shortly. Scott K
diff -Nru ariba-2.14.4+ds/debian/changelog ariba-2.14.4+ds/debian/changelog
--- ariba-2.14.4+ds/debian/changelog 2020-01-24 01:40:24.000000000 -0500
+++ ariba-2.14.4+ds/debian/changelog 2020-03-24 11:14:59.000000000 -0400
@@ -1,3 +1,11 @@
+ariba (2.14.4+ds-2.1) unstable; urgency=medium
+
+ * Non-maintainer upload.
+ * Build for all supported python3 versions to fix test failures in complex
+ Python environments and ease python3 transitions (Closes: #951944)
+
+ -- Scott Kitterman <sc...@kitterman.com> Tue, 24 Mar 2020 11:14:59 -0400
+
ariba (2.14.4+ds-2) unstable; urgency=medium
* Add B-D on dh-python to fix FTBFS.
diff -Nru ariba-2.14.4+ds/debian/control ariba-2.14.4+ds/debian/control
--- ariba-2.14.4+ds/debian/control 2020-01-24 01:40:24.000000000 -0500
+++ ariba-2.14.4+ds/debian/control 2020-03-24 11:13:11.000000000 -0400
@@ -6,7 +6,7 @@
Build-Depends: debhelper-compat (= 12),
dh-python,
python3-biopython,
- python3-dev,
+ python3-all-dev,
python3-dendropy,
python3-setuptools,
python3-pymummer (>= 0.10.2),
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