testscript: only expand second argument to cmpenv (#53)

Author: myitcv

testscript/cmd.go

@@ -133,7 +133,6 @@ func (ts *TestScript) doCmdCmp(args []string, env bool) {
 	text2 = string(data)
 
 	if env {
-		text1 = ts.expand(text1)
 		text2 = ts.expand(text2)
 	}
 

testscript/doc.go

@@ -128,8 +128,8 @@ The predefined commands are:
   (If the files have differing content, the failure prints a diff.)
 
 - cmpenv file1 file2
-  Like cmp, but environment variables are substituted in the file contents
-  before the comparison. For example, $GOOS is replaced by the target GOOS.
+  Like cmp, but environment variables in file2 are substituted before the
+  comparison. For example, $GOOS is replaced by the target GOOS.
 
 - cp src... dst
   Copy the listed files to the target file or existing directory.

testscript/testdata/cmpenv.txt

@@ -0,0 +1,7 @@
+env $=$
+cmpenv file1 file2
+
+-- file1 --
+$i
+-- file2 --
+$$i