1 files changed, 33 insertions, 0 deletions
diff --git a/tests/io.test b/tests/io.test
index f1248b9..a1625ba 100644
--- a/tests/io.test
+++ b/tests/io.test
@@ -1445,6 +1445,39 @@ test io-12.5 {ReadChars: fileevents on partial characters} {stdio openpipe filee
     lappend x [catch {close $f} msg] $msg
     set x
 } "{} timeout {} timeout \u7266 {} eof 0 {}"
+test io-12.6 {ReadChars: too many chars read} {
+    proc driver {cmd args} {
+        variable buffer
+        variable index
+        set chan [lindex $args 0]
+        switch -- $cmd {
+            initialize {
+                set index($chan) 0
+                set buffer($chan) [encoding convertto utf-8 \
+                        [string repeat \uBEEF 20][string repeat . 20]]
+                return {initialize finalize watch read}
+            }
+            finalize {
+                unset index($chan) buffer($chan)
+                return
+            }
+            watch {}
+            read {
+                set n [lindex $args 1]
+                set new [expr {$index($chan) + $n}]
+                set result [string range $buffer($chan) $index($chan) $new-1]
+                set index($chan) $new
+                return $result
+            }
+        }
+    }
+    set c [chan create read [namespace which driver]]
+    chan configure $c -encoding utf-8
+    while {![eof $c]} {
+        read $c 15
+    }
+    close $c
+} {}
 
 test io-13.1 {TranslateInputEOL: cr mode} {} {
     set f [open $path(test1) w]