cmd/internal/obj: add basic test of line history

Change-Id: Ic22e004b43bd98e712befb30684be16d8214c94a
Reviewed-on: https://go-review.googlesource.com/7622Reviewed-by: Rob Pike <r@golang.org>

src/cmd/internal/obj/line_test.go

+// Copyright 2015 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.
+
+package obj
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestLineHist(t *testing.T) {
+	ctxt := new(Link)
+
+	Linklinehist(ctxt, 1, "a.c", 0)
+	Linklinehist(ctxt, 3, "a.h", 0)
+	Linklinehist(ctxt, 5, "<pop>", 0)
+	Linklinehist(ctxt, 7, "linedir", 2)
+	Linklinehist(ctxt, 9, "<pop>", 0)
+	Linklinehist(ctxt, 11, "b.c", 0)
+	Linklinehist(ctxt, 13, "<pop>", 0)
+
+	var expect = []string{
+		0:  "??:0",
+		1:  "/a.c:1",
+		2:  "/a.c:2",
+		3:  "/a.h:1",
+		4:  "/a.h:2",
+		5:  "/a.c:3",
+		6:  "/a.c:4",
+		7:  "/linedir:2",
+		8:  "/linedir:3",
+		9:  "??:0",
+		10: "??:0",
+		11: "/b.c:1",
+		12: "/b.c:2",
+		13: "??:0",
+		14: "??:0",
+	}
+
+	for i, want := range expect {
+		var f *LSym
+		var l int32
+		linkgetline(ctxt, int32(i), &f, &l)
+		have := fmt.Sprintf("%s:%d", f.Name, l)
+		if have != want {
+			t.Errorf("linkgetline(%d) = %q, want %q", i, have, want)
+		}
+	}
+}