Here's a test that works with single-byte encodings: 

>perl -MEncode -wle"for (0..255) { print if chr ne decode($ARGV[0], ch
+r) }" iso-8859-1

>perl -MEncode -wle"for (0x20..0x7E,0x0A..0xFF) { print if chr ne deco
+de($ARGV[0], chr) }" iso-8859-2
161
162
163
165
166
169
...

[download]

Here's a UTF-8 example: 

>perl -MEncode -wle"$chr=qq{\342\231\240}; print 'diff' if $chr ne dec
+ode('UTF-8', $chr)"
diff

[download]

In reply to Re^5: question about Encode::decode('iso-8859-1', ...) by ikegami
in thread question about Encode::decode('iso-8859-1', ...) by perl5ever

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