Issue #15767: Add ModuleNotFoundError.
diff --git a/Lib/test/exception_hierarchy.txt b/Lib/test/exception_hierarchy.txt
index 0513765..7333b2a 100644
--- a/Lib/test/exception_hierarchy.txt
+++ b/Lib/test/exception_hierarchy.txt
@@ -14,6 +14,7 @@
       +-- BufferError
       +-- EOFError
       +-- ImportError
+           +-- ModuleNotFoundError
       +-- LookupError
       |    +-- IndexError
       |    +-- KeyError