don't cover a part of the code that calls external programs
@@ -235,7 +235,7 @@ def to_pdf(a, exact=False,
fline = line.format(to_latex(a, exact=exact, decimals=decimals))
latex = template.format(fline)
- with ExitStack() as stack:
+ with ExitStack() as stack: # pragma: no cover
EC = stack.enter_context
tmpdir = EC(tempdir())
EC(cd(tmpdir))
