test: Add test for //line (currently fails).

R=rsc
CC=golang-dev
https://golang.org/cl/2127045

test/bugs/bug305.go

+// errchk $G $D/$F.go
+
+// Copyright 2010 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Use //line to set the line number of the next line to 20.
+//line bug305.go:20
+
+package p
+
+// Introduce an error which should be reported on line 24.
+var a int = "bogus"
+
+// Line 15 of file.
+// 16
+// 17
+// 18
+// 19
+// 20
+// 21
+// 22
+// 23
+// ERROR "cannot|incompatible"

test/golden.out

@@ -177,3 +177,11 @@ panic PC=xxx
 =========== bugs/bug260.go
 FAIL
 BUG: bug260 failed
+
+=========== bugs/bug305.go
+BUG: errchk: bugs/bug305.go:24: missing expected error: 'cannot|incompatible'
+errchk: bugs/bug305.go: unmatched error messages:
+==================================================
+bug305.go:23[bugs/bug305.go:12]: cannot convert "bogus" to type int
+bug305.go:23[bugs/bug305.go:12]: cannot use "bogus" (type string) as type int in assignment
+==================================================