simplify test_1855 call to 'dot'

Using the wrapper added in 297ed0bc7b61b2a6616c335726334836c8ffcc10, we can
write this code more simply and concisely.

diff --git a/rtest/test_regression.py b/rtest/test_regression.py
index 7672d4e7ac1bd73a8a74405b74e708c8636149e3..5cde878714aaf0bb9910989b404dae09169ad72c 100644 (file)
--- a/rtest/test_regression.py
+++ b/rtest/test_regression.py
@@ -825,7 +825,7 @@ def test_1855():
   assert src.exists(), "unexpectedly missing test case"
 
   # run it through Graphviz
-  svg = subprocess.check_output(["dot", "-Tsvg", src], universal_newlines=True)
+  svg = dot("svg", src)
 
   # find the graph element
   root = ET.fromstring(svg)