diff --git a/beacon-chain/core/helpers/validators_test.go b/beacon-chain/core/helpers/validators_test.go
index d6fa85241..d30f6a9fb 100644
--- a/beacon-chain/core/helpers/validators_test.go
+++ b/beacon-chain/core/helpers/validators_test.go
@@ -1,6 +1,7 @@
 package helpers
 
 import (
+	"reflect"
 	"testing"
 
 	ethpb "github.com/prysmaticlabs/ethereumapis/eth/v1alpha1"
@@ -248,3 +249,159 @@ func TestDomain_OK(t *testing.T) {
 		}
 	}
 }
+
+// Test basic functionality of ActiveValidatorIndices without caching. This test will need to be
+// rewritten when releasing some cache flag.
+func TestActiveValidatorIndices(t *testing.T) {
+	farFutureEpoch := params.BeaconConfig().FarFutureEpoch
+	type args struct {
+		state *pb.BeaconState
+		epoch uint64
+	}
+	tests := []struct {
+		name    string
+		args    args
+		want    []uint64
+		wantErr bool
+	}{
+		{
+			name: "all_active_epoch_10",
+			args: args{
+				state: &pb.BeaconState{
+					Validators: []*ethpb.Validator{
+						&ethpb.Validator{
+							ActivationEpoch: 0,
+							ExitEpoch:       farFutureEpoch,
+						},
+						&ethpb.Validator{
+							ActivationEpoch: 0,
+							ExitEpoch:       farFutureEpoch,
+						},
+						&ethpb.Validator{
+							ActivationEpoch: 0,
+							ExitEpoch:       farFutureEpoch,
+						},
+					},
+				},
+				epoch: 10,
+			},
+			want: []uint64{0, 1, 2},
+		},
+		{
+			name: "some_active_epoch_10",
+			args: args{
+				state: &pb.BeaconState{
+					Validators: []*ethpb.Validator{
+						&ethpb.Validator{
+							ActivationEpoch: 0,
+							ExitEpoch:       farFutureEpoch,
+						},
+						&ethpb.Validator{
+							ActivationEpoch: 0,
+							ExitEpoch:       farFutureEpoch,
+						},
+						&ethpb.Validator{
+							ActivationEpoch: 0,
+							ExitEpoch:       1,
+						},
+					},
+				},
+				epoch: 10,
+			},
+			want: []uint64{0, 1},
+		},
+		{
+			name: "some_active_with_recent_new_epoch_10",
+			args: args{
+				state: &pb.BeaconState{
+					Validators: []*ethpb.Validator{
+						&ethpb.Validator{
+							ActivationEpoch: 0,
+							ExitEpoch:       farFutureEpoch,
+						},
+						&ethpb.Validator{
+							ActivationEpoch: 0,
+							ExitEpoch:       farFutureEpoch,
+						},
+						&ethpb.Validator{
+							ActivationEpoch: 0,
+							ExitEpoch:       1,
+						},
+						&ethpb.Validator{
+							ActivationEpoch: 0,
+							ExitEpoch:       farFutureEpoch,
+						},
+					},
+				},
+				epoch: 10,
+			},
+			want: []uint64{0, 1, 3},
+		},
+		{
+			name: "some_active_with_recent_new_epoch_10",
+			args: args{
+				state: &pb.BeaconState{
+					Validators: []*ethpb.Validator{
+						&ethpb.Validator{
+							ActivationEpoch: 0,
+							ExitEpoch:       farFutureEpoch,
+						},
+						&ethpb.Validator{
+							ActivationEpoch: 0,
+							ExitEpoch:       farFutureEpoch,
+						},
+						&ethpb.Validator{
+							ActivationEpoch: 0,
+							ExitEpoch:       1,
+						},
+						&ethpb.Validator{
+							ActivationEpoch: 0,
+							ExitEpoch:       farFutureEpoch,
+						},
+					},
+				},
+				epoch: 10,
+			},
+			want: []uint64{0, 1, 3},
+		},
+		{
+			name: "some_active_with_recent_new_epoch_10",
+			args: args{
+				state: &pb.BeaconState{
+					Validators: []*ethpb.Validator{
+						&ethpb.Validator{
+							ActivationEpoch: 0,
+							ExitEpoch:       farFutureEpoch,
+						},
+						&ethpb.Validator{
+							ActivationEpoch: 0,
+							ExitEpoch:       1,
+						},
+						&ethpb.Validator{
+							ActivationEpoch: 0,
+							ExitEpoch:       farFutureEpoch,
+						},
+						&ethpb.Validator{
+							ActivationEpoch: 0,
+							ExitEpoch:       farFutureEpoch,
+						},
+					},
+				},
+				epoch: 10,
+			},
+			want: []uint64{0, 2, 3},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := ActiveValidatorIndices(tt.args.state, tt.args.epoch)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("ActiveValidatorIndices() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+			if !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("ActiveValidatorIndices() got = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}