Add unit tests for picker plugin

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

@@ -0,0 +1,135 @@
+/*
+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_test
+
+import (
+	"context"
+	"testing"
+
+	"sigs.k8s.io/gateway-api-inference-extension/pkg/epp/backend"
+	"sigs.k8s.io/gateway-api-inference-extension/pkg/epp/scheduling/framework/plugins/picker"
+	"sigs.k8s.io/gateway-api-inference-extension/pkg/epp/scheduling/types"
+
+	k8stypes "k8s.io/apimachinery/pkg/types"
+)
+
+// Picks the pod with the highest unique score.
+func TestPickMaxScorePicker_SingleMax(t *testing.T) {
+	p := picker.NewMaxScorePicker()
+	ctx := context.Background()
+
+	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,
+		},
+	}
+
+	result := p.Pick(ctx, nil, scoredPods)
+
+	if result == nil {
+		t.Fatal("expected a result but got nil")
+	}
+
+	picked := result.TargetPod.GetPod().NamespacedName.Name
+	if picked != "pod2" {
+		t.Errorf("expected pod2, but got %s", picked)
+	}
+}
+
+// Picks randomly when multiple pods share top score.
+func TestPickMaxScorePicker_MultipleMax(t *testing.T) {
+	p := picker.NewMaxScorePicker()
+	ctx := context.Background()
+
+	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,
+		},
+	}
+
+	result := p.Pick(ctx, nil, scoredPods)
+
+	if result == nil {
+		t.Fatal("expected a result but got nil")
+	}
+
+	picked := result.TargetPod.GetPod().NamespacedName.Name
+	if picked != "podA" && picked != "podB" {
+		t.Errorf("expected podA or podB, but got %s", picked)
+	}
+}
+
+// Returns nil or panics on empty pod list.
+func TestPickMaxScorePicker_EmptyList(t *testing.T) {
+	defer func() {
+		if r := recover(); r != nil {
+			t.Logf("plugin panicked as expected for empty input: %v", r)
+		}
+	}()
+
+	p := picker.NewMaxScorePicker()
+	ctx := context.Background()
+
+	var scoredPods []*types.ScoredPod
+
+	result := p.Pick(ctx, nil, scoredPods)
+	if result != nil {
+		t.Errorf("expected nil result for empty input, got %+v", result)
+	}
+}