Add encoding tests

tests/snippets/encoding.py

@@ -0,0 +1,20 @@
+from testutils import assert_raises
+
+try:
+    b"   \xff".decode("ascii")
+except UnicodeDecodeError as e:
+    assert e.start == 3
+    assert e.end == 4
+else:
+    assert False, "should have thrown UnicodeDecodeError"
+
+assert_raises(UnicodeEncodeError, "¿como estás?".encode, "ascii")
+
+def round_trip(s, encoding="utf-8"):
+    encoded = s.encode(encoding)
+    decoded = encoded.decode(encoding)
+    assert s == decoded
+
+round_trip("👺♦  𝐚Şđƒ  ☆☝")
+round_trip("☢🐣  ᖇ𝓤𝕊тⓟ𝕐𝕥卄σ𝔫  ♬👣")
+round_trip("💀👌  ק𝔂tℍⓞ𝓷 ３  🔥👤")