Move testing utils to its own package

So as not to pollute command-line flags with test.* options.

It appears that importing "testing" (from stdlib) will add flags. To
avoid this, we need code to not depend on testing. But, since
testing_utils was previously in the same package as the rest of the
code, it dragged testing in.

Renaming testing_util.go to e.g., util_for_test.go might be enough to
avoid it being compiled with the regular code. We may want it to be
available to tests for other packages -- after all it is utilities for
testing -- so it goes in its own package.

testing/util.go

@@ -0,0 +1,70 @@
+package testing
+
+import (
+	"fmt"
+	"reflect"
+	"runtime"
+	"strings"
+	"testing"
+)
+
+func CallSite() string {
+	_, file, line, ok := runtime.Caller(2)
+	if ok {
+		// Truncate file name at last file name separator.
+		if index := strings.LastIndex(file, "/"); index >= 0 {
+			file = file[index+1:]
+		} else if index = strings.LastIndex(file, "\\"); index >= 0 {
+			file = file[index+1:]
+		}
+	} else {
+		file = "???"
+		line = 1
+	}
+	return fmt.Sprintf("%s:%d: ", file, line)
+}
+
+func AssertNoErr(t *testing.T, err error) {
+	if err != nil {
+		t.Fatal(CallSite(), err)
+	}
+}
+
+func AssertEqualInt(t *testing.T, got, wanted int, desc string) {
+	if got != wanted {
+		t.Fatalf("%s: Expected %s %d but got %d", CallSite(), desc, wanted, got)
+	}
+}
+
+func AssertEqualString(t *testing.T, got, wanted string, desc string) {
+	if got != wanted {
+		t.Fatalf("%s: Expected %s '%s' but got '%s'", CallSite(), desc, wanted, got)
+	}
+}
+
+func AssertStatus(t *testing.T, got int, wanted int, desc string) {
+	if got != wanted {
+		t.Fatalf("%s: Expected %s %d but got %d", CallSite(), desc, wanted, got)
+	}
+}
+
+func AssertErrorInterface(t *testing.T, got interface{}, wanted interface{}, desc string) {
+	gotT, wantedT := reflect.TypeOf(got), reflect.TypeOf(wanted).Elem()
+	if !gotT.Implements(wantedT) {
+		t.Fatalf("%s: Expected %s but got %s (%s)", CallSite(), wantedT.String(), gotT.String(), desc)
+	}
+}
+
+func AssertErrorType(t *testing.T, got interface{}, wanted interface{}, desc string) {
+	gotT, wantedT := reflect.TypeOf(got), reflect.TypeOf(wanted).Elem()
+	if gotT != wantedT {
+		t.Fatalf("%s: Expected %s but got %s (%s)", CallSite(), wantedT.String(), gotT.String(), desc)
+	}
+}
+
+func AssertType(t *testing.T, got interface{}, wanted interface{}, desc string) {
+	gotT, wantedT := reflect.TypeOf(got), reflect.TypeOf(wanted)
+	if gotT != wantedT {
+		t.Fatalf("%s: Expected %s but got %s (%s)", CallSite(), wantedT.String(), gotT.String(), desc)
+	}
+}