Require exact match when calling Get method within fake clientset

`Get` method within the fake clientset returns an object that would not be normally returned when using the real clientset. Reproducer:

```go
package main

import (
	v1 "k8s.io/api/core/v1"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/client-go/kubernetes/fake"
)

func main () {
	cm := &v1.ConfigMap{
		ObjectMeta: metav1.ObjectMeta{Namespace: metav1.NamespaceSystem, Name: "cm"},
		}

	client := fake.NewSimpleClientset(cm)
	obj, err := client.CoreV1().ConfigMaps("").Get("", metav1.GetOptions{})
	if err != nil {
		panic(err)
	}
	fmt.Printf("obj: %#v\n", obj)
}
```

stored under `test.go` of `github.com/kubernetes/kubernetes` (master HEAD) root directory and ran:

```sh
$ go run test.go
obj: &v1.ConfigMap{TypeMeta:v1.TypeMeta{Kind:"", APIVersion:""}, ObjectMeta:v1.ObjectMeta{Name:"cm", GenerateName:"", Namespace:"kube-system", SelfLink:"", UID:"", ResourceVersion:"", Generation:0, CreationTimestamp:v1.Time{Time:time.Time{wall:0x0, ext:0, loc:(*time.Location)(nil)}}, DeletionTimestamp:(*v1.Time)(nil), DeletionGracePeriodSeconds:(*int64)(nil), Labels:map[string]string(nil), Annotations:map[string]string(nil), OwnerReferences:[]v1.OwnerReference(nil), Finalizers:[]string(nil), ClusterName:"", ManagedFields:[]v1.ManagedFieldsEntry(nil)}, Data:map[string]string(nil), BinaryData:map[string][]uint8(nil)}
```

As you can see fake clientset with a "test" configmap is created. When getting the object through the clientset back, I intentionally set the object name to an empty string. I would expect to get an error saying config map "" was not found. However, I get "test" configmap instead.

Reason for that is inside implementation of `filterByNamespaceAndName` private function:
```go
func filterByNamespaceAndName(objs []runtime.Object, ns, name string) ([]runtime.Object, error) {
	var res []runtime.Object

	for _, obj := range objs {
		acc, err := meta.Accessor(obj)
		if err != nil {
			return nil, err
		}
		if ns != "" && acc.GetNamespace() != ns {
			continue
		}
		if name != "" && acc.GetName() != name {
			continue
		}
		res = append(res, obj)
	}

	return res, nil
}
```

When `name` is empty, `name != "" && acc.GetName() != name` condition is false and thus `obj` is consider as a fit.

[1] https://github.com/kubernetes/client-go/blob/master/testing/fixture.go#L481-L493

Kubernetes-commit: d32c76fc03381784516c47cb1bf62ef932189afa

testing/fixture.go

@@ -248,7 +248,7 @@ func (t *tracker) List(gvr schema.GroupVersionResource, gvk schema.GroupVersionK
 		return list, nil
 	}
 
-	matchingObjs, err := filterByNamespaceAndName(objs, ns, "")
+	matchingObjs, err := filterByNamespace(objs, ns)
 	if err != nil {
 		return nil, err
 	}
@@ -282,10 +282,20 @@ func (t *tracker) Get(gvr schema.GroupVersionResource, ns, name string) (runtime
 		return nil, errNotFound
 	}
 
-	matchingObjs, err := filterByNamespaceAndName(objs, ns, name)
+	var matchingObjs []runtime.Object
+	for _, obj := range objs {
+		acc, err := meta.Accessor(obj)
 		if err != nil {
 			return nil, err
 		}
+		if acc.GetNamespace() != ns {
+			continue
+		}
+		if acc.GetName() != name {
+			continue
+		}
+		matchingObjs = append(matchingObjs, obj)
+	}
 	if len(matchingObjs) == 0 {
 		return nil, errNotFound
 	}
@@ -472,10 +482,10 @@ func (t *tracker) Delete(gvr schema.GroupVersionResource, ns, name string) error
 	return errors.NewNotFound(gvr.GroupResource(), name)
 }
 
-// filterByNamespaceAndName returns all objects in the collection that
-// match provided namespace and name. Empty namespace matches
+// filterByNamespace returns all objects in the collection that
+// match provided namespace. Empty namespace matches
 // non-namespaced objects.
-func filterByNamespaceAndName(objs []runtime.Object, ns, name string) ([]runtime.Object, error) {
+func filterByNamespace(objs []runtime.Object, ns string) ([]runtime.Object, error) {
 	var res []runtime.Object
 
 	for _, obj := range objs {
@@ -486,9 +496,6 @@ func filterByNamespaceAndName(objs []runtime.Object, ns, name string) ([]runtime
 		if ns != "" && acc.GetNamespace() != ns {
 			continue
 		}
-		if name != "" && acc.GetName() != name {
-			continue
-		}
 		res = append(res, obj)
 	}
 

testing/fixture_test.go

@@ -25,6 +25,7 @@ import (
 
 	"github.com/stretchr/testify/assert"
 
+	"k8s.io/apimachinery/pkg/api/errors"
 	"k8s.io/apimachinery/pkg/api/meta"
 	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
 	runtime "k8s.io/apimachinery/pkg/runtime"
@@ -274,3 +275,50 @@ func TestPatchWithMissingObject(t *testing.T) {
 	assert.Nil(t, node)
 	assert.EqualError(t, err, `nodes "node-1" not found`)
 }
+
+func TestGetWithExactMatch(t *testing.T) {
+	scheme := runtime.NewScheme()
+	codecs := serializer.NewCodecFactory(scheme)
+
+	constructObject := func(s schema.GroupVersionResource, name, namespace string) (*unstructured.Unstructured, schema.GroupVersionResource) {
+		obj := getArbitraryResource(s, name, namespace)
+		gvks, _, err := scheme.ObjectKinds(obj)
+		assert.Nil(t, err)
+		gvr, _ := meta.UnsafeGuessKindToResource(gvks[0])
+		return obj, gvr
+	}
+
+	var err error
+	// Object with empty namespace
+	o := NewObjectTracker(scheme, codecs.UniversalDecoder())
+	nodeResource := schema.GroupVersionResource{Group: "", Version: "v1", Resource: "node"}
+	node, gvr := constructObject(nodeResource, "node", "")
+
+	assert.Nil(t, o.Add(node))
+
+	// Exact match
+	_, err = o.Get(gvr, "", "node")
+	assert.Nil(t, err)
+
+	// Unexpected namespace provided
+	_, err = o.Get(gvr, "ns", "node")
+	assert.NotNil(t, err)
+	errNotFound := errors.NewNotFound(gvr.GroupResource(), "node")
+	assert.EqualError(t, err, errNotFound.Error())
+
+	// Object with non-empty namespace
+	o = NewObjectTracker(scheme, codecs.UniversalDecoder())
+	podResource := schema.GroupVersionResource{Group: "", Version: "v1", Resource: "pod"}
+	pod, gvr := constructObject(podResource, "pod", "default")
+	assert.Nil(t, o.Add(pod))
+
+	// Exact match
+	_, err = o.Get(gvr, "default", "pod")
+	assert.Nil(t, err)
+
+	// Missing namespace
+	_, err = o.Get(gvr, "", "pod")
+	assert.NotNil(t, err)
+	errNotFound = errors.NewNotFound(gvr.GroupResource(), "pod")
+	assert.EqualError(t, err, errNotFound.Error())
+}