[spec/bugs] Repro 'readonly' bug in bash found by Travis Everett.

spec/bugs.test.sh

@@ -19,3 +19,42 @@ echo $a
 ## N-I dash/ash stdout-json: ""
 ## N-I dash/ash status: 2
 
+
+#### assign readonly -- one line
+readonly x=1; x=2; echo hi
+## status: 1
+## OK dash/mksh/ash status: 2
+## STDOUT:
+## END
+
+#### assign readonly -- multiple lines
+readonly x=1
+x=2
+echo hi
+## status: 1
+## OK dash/mksh/ash status: 2
+## STDOUT:
+## END
+## BUG bash status: 0
+## BUG bash STDOUT:
+hi
+## END
+
+#### unset readonly -- one line
+readonly x=1; unset x; echo hi
+## STDOUT:
+hi
+## END
+## OK dash/ash status: 2
+## OK zsh status: 1
+## OK dash/ash stdout-json: ""
+## OK zsh stdout-json: ""
+
+#### unset readonly -- multiple lines
+readonly x=1
+unset x
+echo hi
+## OK dash/ash status: 2
+## OK zsh status: 1
+## OK dash/ash stdout-json: ""
+## OK zsh stdout-json: ""