1 files changed, 70 insertions, 0 deletions
diff --git a/tests/helpers.py b/tests/helpers.py
index 09ba485d..9c6a0ad8 100644
--- a/tests/helpers.py
+++ b/tests/helpers.py
@@ -133,3 +133,73 @@ class SuperModuleCleaner(ModuleCleaner):
             shutil.rmtree("__pycache__")
 
         invalidate_import_caches()
+
+
+# Map chars to numbers for arcz_to_arcs
+_arcz_map = {'.': -1}
+_arcz_map.update(dict((c, ord(c) - ord('0')) for c in '123456789'))
+_arcz_map.update(dict(
+    (c, 10 + ord(c) - ord('A')) for c in 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
+))
+
+def arcz_to_arcs(arcz):
+    """Convert a compact textual representation of arcs to a list of pairs.
+
+    The text has space-separated pairs of letters.  Period is -1, 1-9 are
+    1-9, A-Z are 10 through 36.  The resulting list is sorted regardless of
+    the order of the input pairs.
+
+    ".1 12 2." --> [(-1,1), (1,2), (2,-1)]
+
+    Minus signs can be included in the pairs:
+
+    "-11, 12, 2-5" --> [(-1,1), (1,2), (2,-5)]
+
+    """
+    arcs = []
+    for pair in arcz.split():
+        asgn = bsgn = 1
+        if len(pair) == 2:
+            a, b = pair
+        else:
+            assert len(pair) == 3
+            if pair[0] == '-':
+                _, a, b = pair
+                asgn = -1
+            else:
+                assert pair[1] == '-'
+                a, _, b = pair
+                bsgn = -1
+        arcs.append((asgn * _arcz_map[a], bsgn * _arcz_map[b]))
+    return sorted(arcs)
+
+
+_arcz_unmap = {val: ch for ch, val in _arcz_map.items()}
+
+def _arcs_to_arcz_repr_one(num):
+    """Return an arcz form of the number `num`, or "?" if there is none."""
+    if num == -1:
+        return "."
+    z = ""
+    if num < 0:
+        z += "-"
+        num *= -1
+    z += _arcz_unmap.get(num, "?")
+    return z
+
+
+def arcs_to_arcz_repr(arcs):
+    """Convert a list of arcs to a readable multi-line form for asserting.
+
+    Each pair is on its own line, with a comment showing the arcz form,
+    to make it easier to decode when debugging test failures.
+
+    """
+    repr_list = []
+    for a, b in arcs:
+        line = repr((a, b))
+        line += " # "
+        line += _arcs_to_arcz_repr_one(a)
+        line += _arcs_to_arcz_repr_one(b)
+        repr_list.append(line)
+    return "\n".join(repr_list) + "\n"