add test for util.which

* and make runtests.sh dash-compatible for debian-like OS

tests/test_util.py

@@ -2,6 +2,7 @@
 
 import mock
 import unittest
+import re
 
 import tests.mocks as mocks
 
@@ -53,4 +54,12 @@ class TestUtil(unittest.TestCase):
         with self.assertRaises(RuntimeError):
             execute(self.some_command_with_args)
 
+    def test_which(self):
+        program = "iwgetid"
+        self.assertTrue(
+            which(program) is None or 
+            re.search('/(' + program + ')$', which(program))
+        )
+
+
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