tests: Verify branch coverage

l0b0 · l0b0 · commit 377419d11440 · 2021-06-29T15:53:09.000+12:00
Stricter than statement coverage. The coverage library does not yet have support for conditional coverage <nedbat/coveragepy#660>, which is even stricter.
diff --git a/.coveragerc b/.coveragerc
@@ -2,4 +2,5 @@
 fail_under = 91
 
 [run]
+branch = true
 source = pystac
