Add unit tests for picker plugin (#1103)

* Add unit tests for picker plugin

* Fix import formatting in test

* Refactor picker tests to follow table-driven format

Author: pabhi18

pkg/epp/scheduling/framework/plugins/picker/picker_test.go

@@ -0,0 +1,95 @@
+/*
+Copyright 2025 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 picker
+
+import (
+	"context"
+	"testing"
+
+	"sigs.k8s.io/gateway-api-inference-extension/pkg/epp/backend"
+	"sigs.k8s.io/gateway-api-inference-extension/pkg/epp/scheduling/types"
+
+	k8stypes "k8s.io/apimachinery/pkg/types"
+)
+
+func TestPickMaxScorePicker(t *testing.T) {
+	tests := []struct {
+		name        string
+		scoredPods  []*types.ScoredPod
+		wantNames   []string
+		shouldPanic bool
+	}{
+		{
+			name: "Single max score",
+			scoredPods: []*types.ScoredPod{
+				{Pod: &types.PodMetrics{Pod: &backend.Pod{NamespacedName: k8stypes.NamespacedName{Name: "pod1"}}}, Score: 10},
+				{Pod: &types.PodMetrics{Pod: &backend.Pod{NamespacedName: k8stypes.NamespacedName{Name: "pod2"}}}, Score: 25},
+				{Pod: &types.PodMetrics{Pod: &backend.Pod{NamespacedName: k8stypes.NamespacedName{Name: "pod3"}}}, Score: 15},
+			},
+			wantNames: []string{"pod2"},
+		},
+		{
+			name: "Multiple max scores",
+			scoredPods: []*types.ScoredPod{
+				{Pod: &types.PodMetrics{Pod: &backend.Pod{NamespacedName: k8stypes.NamespacedName{Name: "podA"}}}, Score: 50},
+				{Pod: &types.PodMetrics{Pod: &backend.Pod{NamespacedName: k8stypes.NamespacedName{Name: "podB"}}}, Score: 50},
+				{Pod: &types.PodMetrics{Pod: &backend.Pod{NamespacedName: k8stypes.NamespacedName{Name: "podC"}}}, Score: 30},
+			},
+			wantNames: []string{"podA", "podB"},
+		},
+		{
+			name:        "Empty pod list",
+			scoredPods:  []*types.ScoredPod{},
+			wantNames:   nil,
+			shouldPanic: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if tt.shouldPanic {
+				defer func() {
+					if r := recover(); r == nil {
+						t.Errorf("expected panic but did not get one")
+					}
+				}()
+			}
+
+			p := NewMaxScorePicker()
+			result := p.Pick(context.Background(), nil, tt.scoredPods)
+
+			if len(tt.scoredPods) == 0 && result != nil {
+				t.Errorf("expected nil result for empty input, got %+v", result)
+				return
+			}
+
+			if result != nil {
+				got := result.TargetPod.GetPod().NamespacedName.Name
+				match := false
+				for _, want := range tt.wantNames {
+					if got == want {
+						match = true
+						break
+					}
+				}
+				if !match {
+					t.Errorf("got %q, want one of %v", got, tt.wantNames)
+				}
+			}
+		})
+	}
+}