diff --git a/pkg/cmd/set/helper.go b/pkg/cmd/set/helper.go
index a60bcd63..249beaea 100644
--- a/pkg/cmd/set/helper.go
+++ b/pkg/cmd/set/helper.go
@@ -131,6 +131,12 @@ func findEnv(env []v1.EnvVar, name string) (v1.EnvVar, bool) {
 	return v1.EnvVar{}, false
 }
 
+// updateEnv adds and deletes specified environment variables from existing environment variables.
+// An added variable replaces all existing variables with the same name.
+// Removing a variable removes all existing variables with the same name.
+// If the existing list contains duplicates that are unrelated to the variables being added and removed,
+// those duplicates are left intact in the result.
+// If a variable is both added and removed, the removal takes precedence.
 func updateEnv(existing []v1.EnvVar, env []v1.EnvVar, remove []string) []v1.EnvVar {
 	out := []v1.EnvVar{}
 	covered := sets.NewString(remove...)
diff --git a/pkg/cmd/set/helper_test.go b/pkg/cmd/set/helper_test.go
new file mode 100644
index 00000000..35315465
--- /dev/null
+++ b/pkg/cmd/set/helper_test.go
@@ -0,0 +1,123 @@
+/*
+Copyright 2021 The Kubernetes 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 set
+
+import (
+	"reflect"
+	"testing"
+
+	v1 "k8s.io/api/core/v1"
+)
+
+func Test_updateEnv(t *testing.T) {
+	var (
+		env1 = v1.EnvVar{
+			Name:  "env1",
+			Value: "env1",
+		}
+		env2 = v1.EnvVar{
+			Name:  "env2",
+			Value: "env2",
+		}
+		env3 = v1.EnvVar{
+			Name:  "env3",
+			Value: "env3",
+		}
+	)
+
+	type args struct {
+		existing []v1.EnvVar
+		add      []v1.EnvVar
+		remove   []string
+	}
+	tests := []struct {
+		name string
+		args args
+		want []v1.EnvVar
+	}{
+		{
+			name: "case 1: add a new and remove another one",
+			args: args{
+				existing: []v1.EnvVar{env1},
+				add:      []v1.EnvVar{env2},
+				remove:   []string{env1.Name},
+			},
+			want: []v1.EnvVar{env2},
+		},
+		{
+			name: "case 2: in a collection of multiple env, add a new and remove another one",
+			args: args{
+				existing: []v1.EnvVar{env1, env2},
+				add:      []v1.EnvVar{env3},
+				remove:   []string{env1.Name},
+			},
+			want: []v1.EnvVar{env2, env3},
+		},
+		{
+			name: "case 3: items added are deduplicated",
+			args: args{
+				existing: []v1.EnvVar{env1},
+				add:      []v1.EnvVar{env2, env2},
+				remove:   []string{env1.Name},
+			},
+			want: []v1.EnvVar{env2},
+		},
+		{
+			name: "case 4: multi add and single remove",
+			args: args{
+				existing: []v1.EnvVar{env1},
+				add:      []v1.EnvVar{env2, env2, env2, env3},
+				remove:   []string{env1.Name},
+			},
+			want: []v1.EnvVar{env2, env3},
+		},
+		{
+			name: "case 5: add and remove the same env",
+			args: args{
+				existing: []v1.EnvVar{env1},
+				add:      []v1.EnvVar{env2, env1},
+				remove:   []string{env1.Name, env1.Name},
+			},
+			want: []v1.EnvVar{env2},
+		},
+		{
+			name: "case 6: existing duplicate unmodified by unrelated addition",
+			args: args{
+				existing: []v1.EnvVar{env1, env1},
+				add:      []v1.EnvVar{env2},
+				remove:   nil,
+			},
+			want: []v1.EnvVar{env1, env1, env2},
+		},
+		{
+			name: "case 7: existing duplicate removed when added yet again",
+			args: args{
+				existing: []v1.EnvVar{env1, env1, env2},
+				add:      []v1.EnvVar{env1},
+				remove:   nil,
+			},
+			want: []v1.EnvVar{env1, env2},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := updateEnv(tt.args.existing, tt.args.add, tt.args.remove); !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("updateEnv() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}