Improve the coverage of testing/code

[asottile]

One of many branches -- I used the codecov output from #3875 to find these.

[coveralls]

Coverage increased (+0.05%) to 92.641% when pulling 1e8e17c on asottile:improve_test_code into a319674 on pytest-dev:master.

[codecov]

Codecov Report

Merging #3887 into master will increase coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3887      +/-   ##
==========================================
+ Coverage   92.59%   92.64%   +0.05%     
==========================================
  Files          51       51              
  Lines        9960     9960              
==========================================
+ Hits         9222     9227       +5     
+ Misses        738      733       -5

Impacted Files	Coverage Δ
src/_pytest/terminal.py	94.42% <0%> (+0.92%)	⬆️

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