Fix order of operations when setting lease labels

Fixes an edge case where `WithLabels` would overwrite `WithExpiration`
on a lease when using client options.

Signed-off-by: Austin Vazquez <macedonv@amazon.com>

leases/lease_test.go

@@ -0,0 +1,83 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package leases
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestWithLabels(t *testing.T) {
+	type unitTest struct {
+		name     string
+		uut      *Lease
+		labels   map[string]string
+		expected map[string]string
+	}
+
+	addLabelsToEmptyMap := &unitTest{
+		name: "AddLabelsToEmptyMap",
+		uut:  &Lease{},
+		labels: map[string]string{
+			"containerd.io/gc.root": "2015-12-04T00:00:00Z",
+		},
+		expected: map[string]string{
+			"containerd.io/gc.root": "2015-12-04T00:00:00Z",
+		},
+	}
+
+	addLabelsToNonEmptyMap := &unitTest{
+		name: "AddLabelsToNonEmptyMap",
+		uut: &Lease{
+			Labels: map[string]string{
+				"containerd.io/gc.expire": "2015-12-05T00:00:00Z",
+			},
+		},
+		labels: map[string]string{
+			"containerd.io/gc.root":                   "2015-12-04T00:00:00Z",
+			"containerd.io/gc.ref.snapshot.overlayfs": "sha256:87806a591ce894ff5c699c28fe02093d6cdadd6b1ad86819acea05ccb212ff3d",
+		},
+		expected: map[string]string{
+			"containerd.io/gc.root":                   "2015-12-04T00:00:00Z",
+			"containerd.io/gc.ref.snapshot.overlayfs": "sha256:87806a591ce894ff5c699c28fe02093d6cdadd6b1ad86819acea05ccb212ff3d",
+			"containerd.io/gc.expire":                 "2015-12-05T00:00:00Z",
+		},
+	}
+
+	testcases := []*unitTest{
+		addLabelsToEmptyMap,
+		addLabelsToNonEmptyMap,
+	}
+
+	for _, testcase := range testcases {
+		testcase := testcase
+
+		t.Run(testcase.name, func(t *testing.T) {
+			f := WithLabels(testcase.labels)
+
+			err := f(testcase.uut)
+			require.NoError(t, err)
+
+			for k, v := range testcase.expected {
+				assert.Contains(t, testcase.uut.Labels, k)
+				assert.Equal(t, v, testcase.uut.Labels[k])
+			}
+		})
+	}
+}