testing: use temp dir without symlinks in TestChdir/relative

When paths with symlinks are involved, it's not viable to compare them
with string equality. Don't use a temporary directory with symlinks in
it as input, so the test works in more environments.

For #62516.

Change-Id: I95d774365cc2f90eb0ffcffa61229ed5cee43e3e
Reviewed-on: https://go-review.googlesource.com/c/go/+/607035
Reviewed-by: Ian Lance Taylor <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Auto-Submit: Dmitri Shuralyov <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: dmitshur

src/testing/testing_test.go

@@ -293,7 +293,11 @@ func TestChdir(t *testing.T) {
 	}
 	defer os.Chdir(oldDir)
 
-	tmp := t.TempDir()
+	// The "relative" test case relies on tmp not being a symlink.
+	tmp, err := filepath.EvalSymlinks(t.TempDir())
+	if err != nil {
+		t.Fatal(err)
+	}
 	rel, err := filepath.Rel(oldDir, tmp)
 	if err != nil {
 		t.Fatal(err)