test(gateway): expand BackendLBPolicy tests with circuit breaker

- CircuitBreaker config roundtrip with DeepCopy
- Full policy with load balancing + circuit breaker
- Nil MaxInflightRequests test
- Coverage: 13.9% -> 23.1%

Author: mahmut-Abi

internal/gwexp/backendlb/types_test.go

@@ -23,4 +23,71 @@ func TestDeepCopyRoundtrip(t *testing.T) {
 	copied := original.DeepCopy()
 	assert.Equal(t, original, copied)
 	assert.NotSame(t, original, copied)
+}
+
+func TestBackendLBPolicyWithCircuitBreaker(t *testing.T) {
+	maxInflight := int32(100)
+	policy := &BackendLBPolicy{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:      "cb-policy",
+			Namespace: "default",
+		},
+		Spec: BackendLBPolicySpec{
+			TargetRefs: []LocalPolicyTargetReference{
+				{Group: "", Kind: "Service", Name: "backend-svc"},
+			},
+			CircuitBreaker: &CircuitBreakerConfig{
+				MaxInflightRequests: &maxInflight,
+			},
+		},
+	}
+
+	assert.Equal(t, int32(100), *policy.Spec.CircuitBreaker.MaxInflightRequests)
+	assert.Len(t, policy.Spec.TargetRefs, 1)
+	assert.Equal(t, "backend-svc", string(policy.Spec.TargetRefs[0].Name))
+
+	copied := policy.DeepCopy()
+	assert.Equal(t, policy.Spec.CircuitBreaker.MaxInflightRequests, copied.Spec.CircuitBreaker.MaxInflightRequests)
+}
+
+func TestBackendLBPolicyWithAllFeatures(t *testing.T) {
+	maxInflight := int32(50)
+	lbType := LoadBalancingStrategyTypeConsistentHash
+	hashKeyType := HashKeyTypeHeader
+	headerName := "x-tenant-id"
+
+	policy := &BackendLBPolicy{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:      "full-policy",
+			Namespace: "default",
+		},
+		Spec: BackendLBPolicySpec{
+			TargetRefs: []LocalPolicyTargetReference{
+				{Group: "", Kind: "Service", Name: "api-svc"},
+			},
+			LoadBalancing: &LoadBalancingPolicy{
+				Type: &lbType,
+				ConsistentHash: &ConsistentHashPolicy{
+					KeyType:    &hashKeyType,
+					HeaderName: &headerName,
+				},
+			},
+			CircuitBreaker: &CircuitBreakerConfig{
+				MaxInflightRequests: &maxInflight,
+			},
+		},
+	}
+
+	assert.NotNil(t, policy.Spec.LoadBalancing)
+	assert.Equal(t, LoadBalancingStrategyTypeConsistentHash, *policy.Spec.LoadBalancing.Type)
+	assert.NotNil(t, policy.Spec.CircuitBreaker)
+	assert.Equal(t, int32(50), *policy.Spec.CircuitBreaker.MaxInflightRequests)
+
+	copied := policy.DeepCopy()
+	assert.Equal(t, policy, copied)
+}
+
+func TestCircuitBreakerConfig_NilMaxInflight(t *testing.T) {
+	cfg := &CircuitBreakerConfig{}
+	assert.Nil(t, cfg.MaxInflightRequests)
 }