tests: Catch ValueError instead of any exception to properly test error.
diff --git a/tests/extmod/ubinascii_a2b_base64.py b/tests/extmod/ubinascii_a2b_base64.py
index 1f10b5a..25986b7 100644
--- a/tests/extmod/ubinascii_a2b_base64.py
+++ b/tests/extmod/ubinascii_a2b_base64.py
@@ -18,17 +18,17 @@
 
 try:
     print(binascii.a2b_base64(b'abc'))
-except:
-    print("caught")
+except ValueError:
+    print("ValueError")
 try:
     print(binascii.a2b_base64(b'abcde='))
-except:
-    print("caught")
+except ValueError:
+    print("ValueError")
 try:
     print(binascii.a2b_base64(b'ab*d'))
-except:
-    print("caught")
+except ValueError:
+    print("ValueError")
 try:
     print(binascii.a2b_base64(b'ab=cdef='))
-except:
-    print("caught")
+except ValueError:
+    print("ValueError")