add Reduce tests

Author: reusee

reducer.go

@@ -1,6 +1,7 @@
 package dscope
 
 import (
+	"errors"
 	"fmt"
 	"reflect"
 	"strings"
@@ -12,9 +13,11 @@ type Reducer interface {
 
 var reducerType = reflect.TypeOf((*Reducer)(nil)).Elem()
 
+var ErrNoValues = errors.New("no values")
+
 func Reduce(vs []reflect.Value) reflect.Value {
 	if len(vs) == 0 {
-		panic("no values")
+		panic(ErrNoValues)
 	}
 
 	t := vs[0].Type()
@@ -68,7 +71,7 @@ func Reduce(vs []reflect.Value) reflect.Value {
 		ret = reflect.New(t).Elem()
 		ret.SetInt(i)
 
-	default:
+	default: // NOCOVER
 		panic(fmt.Errorf("don't know how to reduce %v", t))
 	}
 

reducer_test.go

@@ -0,0 +1,45 @@
+package dscope
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestReduceNil(t *testing.T) {
+	func() {
+		defer func() {
+			p := recover()
+			if p == nil {
+				t.Fatal("should panic")
+			}
+			err, ok := p.(error)
+			if !ok {
+				t.Fatal()
+			}
+			if !is(err, ErrNoValues) {
+				t.Fatal()
+			}
+		}()
+		Reduce(nil)
+	}()
+}
+
+func TestReduceMap(t *testing.T) {
+	m := Reduce([]reflect.Value{
+		reflect.ValueOf(map[int]int{
+			1: 2,
+		}),
+		reflect.ValueOf(map[int]int{
+			3: 4,
+		}),
+	}).Interface().(map[int]int)
+	if len(m) != 2 {
+		t.Fatal()
+	}
+	if m[1] != 2 {
+		t.Fatal()
+	}
+	if m[3] != 4 {
+		t.Fatal()
+	}
+}