Passing the wrong type of sequence to M\ encoder write now throws an error

basis/io/files/unique/unique-tests.factor

@@ -5,7 +5,7 @@ IN: io.files.unique.tests
 
 [ 123 ] [
     "core" ".test" [
-        [ [ 123 CHAR: a <repetition> ] dip ascii set-file-contents ]
+        [ [ 123 CHAR: a <string> ] dip ascii set-file-contents ]
         [ file-info size>> ] bi
     ] cleanup-unique-file
 ] unit-test

core/io/encodings/encodings.factor

@@ -130,7 +130,9 @@ M: encoder stream-element-type
 M: encoder stream-write1
     >encoder< encode-char ;
 
-: encoder-write ( string stream encoding -- )
+GENERIC# encoder-write 2 ( string stream encoding -- )
+
+M: string encoder-write
     [ encode-char ] 2curry each ;
 
 M: encoder stream-write

core/io/files/files-tests.factor

@@ -1,7 +1,7 @@
 USING: arrays debugger.threads destructors io io.directories
 io.encodings.8-bit io.encodings.ascii io.encodings.binary
 io.files io.files.private io.files.temp io.files.unique kernel
-make math sequences system threads tools.test ;
+make math sequences system threads tools.test generic.standard ;
 IN: io.files.tests
 
 \ exists? must-infer
@@ -144,3 +144,15 @@ USE: debugger.threads
         -10 seek-absolute seek-input
     ] with-file-reader
 ] must-fail
+
+[
+    "non-string-error" unique-file ascii [
+        { } write
+    ] with-file-writer
+] [ no-method? ] must-fail-with
+
+[
+    "non-byte-array-error" unique-file binary [
+        "" write
+    ] with-file-writer
+] [ no-method? ] must-fail-with