diff --git a/fs_mgr/libsnapshot/Android.bp b/fs_mgr/libsnapshot/Android.bp
index 05e6336..384595d 100644
--- a/fs_mgr/libsnapshot/Android.bp
+++ b/fs_mgr/libsnapshot/Android.bp
@@ -72,6 +72,7 @@
         "device_info.cpp",
         "snapshot.cpp",
         "snapshot_stats.cpp",
+        "snapshot_stub.cpp",
         "snapshot_metadata_updater.cpp",
         "partition_cow_creator.cpp",
         "return.cpp",
diff --git a/fs_mgr/libsnapshot/include/libsnapshot/mock_device_info.h b/fs_mgr/libsnapshot/include/libsnapshot/mock_device_info.h
new file mode 100644
index 0000000..ef9d648
--- /dev/null
+++ b/fs_mgr/libsnapshot/include/libsnapshot/mock_device_info.h
@@ -0,0 +1,37 @@
+// Copyright (C) 2020 The Android Open Source Project
+//
+// 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.
+
+#pragma once
+
+#include <libsnapshot/snapshot.h>
+
+#include <gmock/gmock.h>
+
+namespace android::snapshot {
+
+class MockDeviceInfo : public SnapshotManager::IDeviceInfo {
+  public:
+    MOCK_METHOD(std::string, GetGsidDir, (), (const, override));
+    MOCK_METHOD(std::string, GetMetadataDir, (), (const, override));
+    MOCK_METHOD(std::string, GetSlotSuffix, (), (const, override));
+    MOCK_METHOD(std::string, GetOtherSlotSuffix, (), (const, override));
+    MOCK_METHOD(std::string, GetSuperDevice, (uint32_t slot), (const, override));
+    MOCK_METHOD(const android::fs_mgr::IPartitionOpener&, GetPartitionOpener, (), (const));
+    MOCK_METHOD(bool, IsOverlayfsSetup, (), (const, override));
+    MOCK_METHOD(bool, SetBootControlMergeStatus, (MergeStatus status), (override));
+    MOCK_METHOD(bool, SetSlotAsUnbootable, (unsigned int slot), (override));
+    MOCK_METHOD(bool, IsRecovery, (), (const, override));
+};
+
+}  // namespace android::snapshot
diff --git a/fs_mgr/libsnapshot/include/libsnapshot/mock_snapshot.h b/fs_mgr/libsnapshot/include/libsnapshot/mock_snapshot.h
new file mode 100644
index 0000000..758d66c
--- /dev/null
+++ b/fs_mgr/libsnapshot/include/libsnapshot/mock_snapshot.h
@@ -0,0 +1,54 @@
+// Copyright (C) 2020 The Android Open Source Project
+//
+// 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.
+
+#pragma once
+
+#include <libsnapshot/snapshot.h>
+
+#include <gmock/gmock.h>
+
+namespace android::snapshot {
+
+class MockSnapshotManager : public ISnapshotManager {
+  public:
+    MOCK_METHOD(bool, BeginUpdate, (), (override));
+    MOCK_METHOD(bool, CancelUpdate, (), (override));
+    MOCK_METHOD(bool, FinishedSnapshotWrites, (bool wipe), (override));
+    MOCK_METHOD(bool, InitiateMerge, (), (override));
+
+    MOCK_METHOD(UpdateState, ProcessUpdateState,
+                (const std::function<bool()>& callback, const std::function<bool()>& before_cancel),
+                (override));
+    MOCK_METHOD(UpdateState, GetUpdateState, (double* progress), (override));
+    MOCK_METHOD(Return, CreateUpdateSnapshots,
+                (const chromeos_update_engine::DeltaArchiveManifest& manifest), (override));
+    MOCK_METHOD(bool, MapUpdateSnapshot,
+                (const android::fs_mgr::CreateLogicalPartitionParams& params,
+                 std::string* snapshot_path),
+                (override));
+    MOCK_METHOD(bool, UnmapUpdateSnapshot, (const std::string& target_partition_name), (override));
+    MOCK_METHOD(bool, NeedSnapshotsInFirstStageMount, (), (override));
+    MOCK_METHOD(bool, CreateLogicalAndSnapshotPartitions,
+                (const std::string& super_device, const std::chrono::milliseconds& timeout_ms),
+                (override));
+    MOCK_METHOD(bool, HandleImminentDataWipe, (const std::function<void()>& callback), (override));
+    MOCK_METHOD(CreateResult, RecoveryCreateSnapshotDevices, (), (override));
+    MOCK_METHOD(CreateResult, RecoveryCreateSnapshotDevices,
+                (const std::unique_ptr<AutoDevice>& metadata_device), (override));
+    MOCK_METHOD(bool, Dump, (std::ostream & os), (override));
+    MOCK_METHOD(std::unique_ptr<AutoDevice>, EnsureMetadataMounted, (), (override));
+    MOCK_METHOD(ISnapshotMergeStats*, GetSnapshotMergeStatsInstance, (), (override));
+};
+
+}  // namespace android::snapshot
diff --git a/fs_mgr/libsnapshot/include/libsnapshot/snapshot.h b/fs_mgr/libsnapshot/include/libsnapshot/snapshot.h
index 1daa83b..fff667e 100644
--- a/fs_mgr/libsnapshot/include/libsnapshot/snapshot.h
+++ b/fs_mgr/libsnapshot/include/libsnapshot/snapshot.h
@@ -70,6 +70,8 @@
 struct AutoDeleteSnapshot;
 struct AutoDeviceList;
 struct PartitionCowCreator;
+class ISnapshotMergeStats;
+class SnapshotMergeStats;
 class SnapshotStatus;
 
 static constexpr const std::string_view kCowGroupName = "cow";
@@ -83,17 +85,7 @@
     NOT_CREATED,
 };
 
-class SnapshotManager final {
-    using CreateLogicalPartitionParams = android::fs_mgr::CreateLogicalPartitionParams;
-    using IPartitionOpener = android::fs_mgr::IPartitionOpener;
-    using LpMetadata = android::fs_mgr::LpMetadata;
-    using MetadataBuilder = android::fs_mgr::MetadataBuilder;
-    using DeltaArchiveManifest = chromeos_update_engine::DeltaArchiveManifest;
-    using MergeStatus = android::hardware::boot::V1_1::MergeStatus;
-    using FiemapStatus = android::fiemap::FiemapStatus;
-
-    friend class SnapshotMergeStats;
-
+class ISnapshotManager {
   public:
     // Dependency injection for testing.
     class IDeviceInfo {
@@ -104,39 +96,23 @@
         virtual std::string GetSlotSuffix() const = 0;
         virtual std::string GetOtherSlotSuffix() const = 0;
         virtual std::string GetSuperDevice(uint32_t slot) const = 0;
-        virtual const IPartitionOpener& GetPartitionOpener() const = 0;
+        virtual const android::fs_mgr::IPartitionOpener& GetPartitionOpener() const = 0;
         virtual bool IsOverlayfsSetup() const = 0;
-        virtual bool SetBootControlMergeStatus(MergeStatus status) = 0;
+        virtual bool SetBootControlMergeStatus(
+                android::hardware::boot::V1_1::MergeStatus status) = 0;
         virtual bool SetSlotAsUnbootable(unsigned int slot) = 0;
         virtual bool IsRecovery() const = 0;
     };
-
-    ~SnapshotManager();
-
-    // Return a new SnapshotManager instance, or null on error. The device
-    // pointer is owned for the lifetime of SnapshotManager. If null, a default
-    // instance will be created.
-    static std::unique_ptr<SnapshotManager> New(IDeviceInfo* device = nullptr);
-
-    // This is similar to New(), except designed specifically for first-stage
-    // init or recovery.
-    static std::unique_ptr<SnapshotManager> NewForFirstStageMount(IDeviceInfo* device = nullptr);
-
-    // Helper function for first-stage init to check whether a SnapshotManager
-    // might be needed to perform first-stage mounts.
-    static bool IsSnapshotManagerNeeded();
-
-    // Helper function for second stage init to restorecon on the rollback indicator.
-    static std::string GetGlobalRollbackIndicatorPath();
+    virtual ~ISnapshotManager() = default;
 
     // Begin an update. This must be called before creating any snapshots. It
     // will fail if GetUpdateState() != None.
-    bool BeginUpdate();
+    virtual bool BeginUpdate() = 0;
 
     // Cancel an update; any snapshots will be deleted. This is allowed if the
     // state == Initiated, None, or Unverified (before rebooting to the new
     // slot).
-    bool CancelUpdate();
+    virtual bool CancelUpdate() = 0;
 
     // Mark snapshot writes as having completed. After this, new snapshots cannot
     // be created, and the device must either cancel the OTA (either before
@@ -144,11 +120,11 @@
     // Before calling this function, all snapshots must be mapped.
     // If |wipe| is set to true, wipe is scheduled after reboot, and snapshots
     // may need to be merged before wiping.
-    bool FinishedSnapshotWrites(bool wipe);
+    virtual bool FinishedSnapshotWrites(bool wipe) = 0;
 
     // Initiate a merge on all snapshot devices. This should only be used after an
     // update has been marked successful after booting.
-    bool InitiateMerge();
+    virtual bool InitiateMerge() = 0;
 
     // Perform any necessary post-boot actions. This should be run soon after
     // /data is mounted.
@@ -178,8 +154,8 @@
     //
     // The optional callback allows the caller to periodically check the
     // progress with GetUpdateState().
-    UpdateState ProcessUpdateState(const std::function<bool()>& callback = {},
-                                   const std::function<bool()>& before_cancel = {});
+    virtual UpdateState ProcessUpdateState(const std::function<bool()>& callback = {},
+                                           const std::function<bool()>& before_cancel = {}) = 0;
 
     // Find the status of the current update, if any.
     //
@@ -187,28 +163,30 @@
     //   Merging: Value in the range [0, 100]
     //   MergeCompleted: 100
     //   Other: 0
-    UpdateState GetUpdateState(double* progress = nullptr);
+    virtual UpdateState GetUpdateState(double* progress = nullptr) = 0;
 
     // Create necessary COW device / files for OTA clients. New logical partitions will be added to
     // group "cow" in target_metadata. Regions of partitions of current_metadata will be
     // "write-protected" and snapshotted.
-    Return CreateUpdateSnapshots(const DeltaArchiveManifest& manifest);
+    virtual Return CreateUpdateSnapshots(
+            const chromeos_update_engine::DeltaArchiveManifest& manifest) = 0;
 
     // Map a snapshotted partition for OTA clients to write to. Write-protected regions are
     // determined previously in CreateSnapshots.
-    bool MapUpdateSnapshot(const CreateLogicalPartitionParams& params, std::string* snapshot_path);
+    virtual bool MapUpdateSnapshot(const android::fs_mgr::CreateLogicalPartitionParams& params,
+                                   std::string* snapshot_path) = 0;
 
     // Unmap a snapshot device that's previously mapped with MapUpdateSnapshot.
-    bool UnmapUpdateSnapshot(const std::string& target_partition_name);
+    virtual bool UnmapUpdateSnapshot(const std::string& target_partition_name) = 0;
 
     // If this returns true, first-stage mount must call
     // CreateLogicalAndSnapshotPartitions rather than CreateLogicalPartitions.
-    bool NeedSnapshotsInFirstStageMount();
+    virtual bool NeedSnapshotsInFirstStageMount() = 0;
 
     // Perform first-stage mapping of snapshot targets. This replaces init's
     // call to CreateLogicalPartitions when snapshots are present.
-    bool CreateLogicalAndSnapshotPartitions(const std::string& super_device,
-                                            const std::chrono::milliseconds& timeout_ms = {});
+    virtual bool CreateLogicalAndSnapshotPartitions(
+            const std::string& super_device, const std::chrono::milliseconds& timeout_ms = {}) = 0;
 
     // This method should be called preceding any wipe or flash of metadata or
     // userdata. It is only valid in recovery or fastbootd, and it ensures that
@@ -221,7 +199,7 @@
     //
     // Returns true on success (or nothing to do), false on failure. The
     // optional callback fires periodically to query progress via GetUpdateState.
-    bool HandleImminentDataWipe(const std::function<void()>& callback = {});
+    virtual bool HandleImminentDataWipe(const std::function<void()>& callback = {}) = 0;
 
     // This method is only allowed in recovery and is used as a helper to
     // initialize the snapshot devices as a requirement to mount a snapshotted
@@ -234,14 +212,15 @@
     // be aborted.
     // This function mounts /metadata when called, and unmounts /metadata upon
     // return.
-    CreateResult RecoveryCreateSnapshotDevices();
+    virtual CreateResult RecoveryCreateSnapshotDevices() = 0;
 
     // Same as RecoveryCreateSnapshotDevices(), but does not auto mount/umount
     // /metadata.
-    CreateResult RecoveryCreateSnapshotDevices(const std::unique_ptr<AutoDevice>& metadata_device);
+    virtual CreateResult RecoveryCreateSnapshotDevices(
+            const std::unique_ptr<AutoDevice>& metadata_device) = 0;
 
     // Dump debug information.
-    bool Dump(std::ostream& os);
+    virtual bool Dump(std::ostream& os) = 0;
 
     // Ensure metadata directory is mounted in recovery. When the returned
     // AutoDevice is destroyed, the metadata directory is automatically
@@ -257,7 +236,65 @@
     //   auto b = mgr->EnsureMetadataMounted(); // does nothing
     //   b.reset() // unmounts
     //   a.reset() // does nothing
-    std::unique_ptr<AutoDevice> EnsureMetadataMounted();
+    virtual std::unique_ptr<AutoDevice> EnsureMetadataMounted() = 0;
+
+    // Return the associated ISnapshotMergeStats instance. Never null.
+    virtual ISnapshotMergeStats* GetSnapshotMergeStatsInstance() = 0;
+};
+
+class SnapshotManager final : public ISnapshotManager {
+    using CreateLogicalPartitionParams = android::fs_mgr::CreateLogicalPartitionParams;
+    using IPartitionOpener = android::fs_mgr::IPartitionOpener;
+    using LpMetadata = android::fs_mgr::LpMetadata;
+    using MetadataBuilder = android::fs_mgr::MetadataBuilder;
+    using DeltaArchiveManifest = chromeos_update_engine::DeltaArchiveManifest;
+    using MergeStatus = android::hardware::boot::V1_1::MergeStatus;
+    using FiemapStatus = android::fiemap::FiemapStatus;
+
+    friend class SnapshotMergeStats;
+
+  public:
+    ~SnapshotManager();
+
+    // Return a new SnapshotManager instance, or null on error. The device
+    // pointer is owned for the lifetime of SnapshotManager. If null, a default
+    // instance will be created.
+    static std::unique_ptr<SnapshotManager> New(IDeviceInfo* device = nullptr);
+
+    // This is similar to New(), except designed specifically for first-stage
+    // init or recovery.
+    static std::unique_ptr<SnapshotManager> NewForFirstStageMount(IDeviceInfo* device = nullptr);
+
+    // Helper function for first-stage init to check whether a SnapshotManager
+    // might be needed to perform first-stage mounts.
+    static bool IsSnapshotManagerNeeded();
+
+    // Helper function for second stage init to restorecon on the rollback indicator.
+    static std::string GetGlobalRollbackIndicatorPath();
+
+    // ISnapshotManager overrides.
+    bool BeginUpdate() override;
+    bool CancelUpdate() override;
+    bool FinishedSnapshotWrites(bool wipe) override;
+    bool InitiateMerge() override;
+    UpdateState ProcessUpdateState(const std::function<bool()>& callback = {},
+                                   const std::function<bool()>& before_cancel = {}) override;
+    UpdateState GetUpdateState(double* progress = nullptr) override;
+    Return CreateUpdateSnapshots(const DeltaArchiveManifest& manifest) override;
+    bool MapUpdateSnapshot(const CreateLogicalPartitionParams& params,
+                           std::string* snapshot_path) override;
+    bool UnmapUpdateSnapshot(const std::string& target_partition_name) override;
+    bool NeedSnapshotsInFirstStageMount() override;
+    bool CreateLogicalAndSnapshotPartitions(
+            const std::string& super_device,
+            const std::chrono::milliseconds& timeout_ms = {}) override;
+    bool HandleImminentDataWipe(const std::function<void()>& callback = {}) override;
+    CreateResult RecoveryCreateSnapshotDevices() override;
+    CreateResult RecoveryCreateSnapshotDevices(
+            const std::unique_ptr<AutoDevice>& metadata_device) override;
+    bool Dump(std::ostream& os) override;
+    std::unique_ptr<AutoDevice> EnsureMetadataMounted() override;
+    ISnapshotMergeStats* GetSnapshotMergeStatsInstance() override;
 
   private:
     FRIEND_TEST(SnapshotTest, CleanFirstStageMount);
diff --git a/fs_mgr/libsnapshot/include/libsnapshot/snapshot_stats.h b/fs_mgr/libsnapshot/include/libsnapshot/snapshot_stats.h
index 91dd34f..4caf632 100644
--- a/fs_mgr/libsnapshot/include/libsnapshot/snapshot_stats.h
+++ b/fs_mgr/libsnapshot/include/libsnapshot/snapshot_stats.h
@@ -23,14 +23,12 @@
 namespace android {
 namespace snapshot {
 
-class SnapshotMergeStats {
+class ISnapshotMergeStats {
   public:
-    // Not thread safe.
-    static SnapshotMergeStats* GetInstance(SnapshotManager& manager);
-
+    virtual ~ISnapshotMergeStats() = default;
     // Called when merge starts or resumes.
-    bool Start();
-    void set_state(android::snapshot::UpdateState state);
+    virtual bool Start() = 0;
+    virtual void set_state(android::snapshot::UpdateState state) = 0;
 
     // Called when merge ends. Properly clean up permanent storage.
     class Result {
@@ -40,7 +38,19 @@
         // Time between successful Start() / Resume() to Finish().
         virtual std::chrono::steady_clock::duration merge_time() const = 0;
     };
-    std::unique_ptr<Result> Finish();
+    // Return nullptr if any failure.
+    virtual std::unique_ptr<Result> Finish() = 0;
+};
+
+class SnapshotMergeStats : public ISnapshotMergeStats {
+  public:
+    // Not thread safe.
+    static SnapshotMergeStats* GetInstance(SnapshotManager& manager);
+
+    // ISnapshotMergeStats overrides
+    bool Start() override;
+    void set_state(android::snapshot::UpdateState state) override;
+    std::unique_ptr<Result> Finish() override;
 
   private:
     bool ReadState();
diff --git a/fs_mgr/libsnapshot/include/libsnapshot/snapshot_stub.h b/fs_mgr/libsnapshot/include/libsnapshot/snapshot_stub.h
new file mode 100644
index 0000000..9b2590c
--- /dev/null
+++ b/fs_mgr/libsnapshot/include/libsnapshot/snapshot_stub.h
@@ -0,0 +1,52 @@
+// Copyright (C) 2020 The Android Open Source Project
+//
+// 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.
+
+#pragma once
+
+#include <libsnapshot/snapshot.h>
+
+namespace android::snapshot {
+
+class SnapshotManagerStub : public ISnapshotManager {
+  public:
+    // Create a stubbed snapshot manager. All calls into the stub fails.
+    static std::unique_ptr<ISnapshotManager> New();
+
+    // ISnapshotManager overrides.
+    bool BeginUpdate() override;
+    bool CancelUpdate() override;
+    bool FinishedSnapshotWrites(bool wipe) override;
+    bool InitiateMerge() override;
+    UpdateState ProcessUpdateState(const std::function<bool()>& callback = {},
+                                   const std::function<bool()>& before_cancel = {}) override;
+    UpdateState GetUpdateState(double* progress = nullptr) override;
+    Return CreateUpdateSnapshots(
+            const chromeos_update_engine::DeltaArchiveManifest& manifest) override;
+    bool MapUpdateSnapshot(const android::fs_mgr::CreateLogicalPartitionParams& params,
+                           std::string* snapshot_path) override;
+    bool UnmapUpdateSnapshot(const std::string& target_partition_name) override;
+    bool NeedSnapshotsInFirstStageMount() override;
+    bool CreateLogicalAndSnapshotPartitions(
+            const std::string& super_device,
+            const std::chrono::milliseconds& timeout_ms = {}) override;
+    bool HandleImminentDataWipe(const std::function<void()>& callback = {}) override;
+    CreateResult RecoveryCreateSnapshotDevices() override;
+    CreateResult RecoveryCreateSnapshotDevices(
+            const std::unique_ptr<AutoDevice>& metadata_device) override;
+    bool Dump(std::ostream& os) override;
+    std::unique_ptr<AutoDevice> EnsureMetadataMounted() override;
+    ISnapshotMergeStats* GetSnapshotMergeStatsInstance() override;
+};
+
+}  // namespace android::snapshot
diff --git a/fs_mgr/libsnapshot/snapshot.cpp b/fs_mgr/libsnapshot/snapshot.cpp
index c9fa28e..eafeea2 100644
--- a/fs_mgr/libsnapshot/snapshot.cpp
+++ b/fs_mgr/libsnapshot/snapshot.cpp
@@ -2685,5 +2685,9 @@
     return true;
 }
 
+ISnapshotMergeStats* SnapshotManager::GetSnapshotMergeStatsInstance() {
+    return SnapshotMergeStats::GetInstance(*this);
+}
+
 }  // namespace snapshot
 }  // namespace android
diff --git a/fs_mgr/libsnapshot/snapshot_stub.cpp b/fs_mgr/libsnapshot/snapshot_stub.cpp
new file mode 100644
index 0000000..2747b03
--- /dev/null
+++ b/fs_mgr/libsnapshot/snapshot_stub.cpp
@@ -0,0 +1,125 @@
+// Copyright (C) 2020 The Android Open Source Project
+//
+// 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.
+
+#include <libsnapshot/snapshot_stub.h>
+
+#include <android-base/logging.h>
+
+#include <libsnapshot/snapshot_stats.h>
+
+using android::fs_mgr::CreateLogicalPartitionParams;
+using chromeos_update_engine::DeltaArchiveManifest;
+
+namespace android::snapshot {
+
+std::unique_ptr<ISnapshotManager> SnapshotManagerStub::New() {
+    return std::make_unique<SnapshotManagerStub>();
+}
+
+bool SnapshotManagerStub::BeginUpdate() {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return false;
+}
+
+bool SnapshotManagerStub::CancelUpdate() {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return false;
+}
+
+bool SnapshotManagerStub::FinishedSnapshotWrites(bool) {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return false;
+}
+
+bool SnapshotManagerStub::InitiateMerge() {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return false;
+}
+
+UpdateState SnapshotManagerStub::ProcessUpdateState(const std::function<bool()>&,
+                                                    const std::function<bool()>&) {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return UpdateState::None;
+}
+
+UpdateState SnapshotManagerStub::GetUpdateState(double*) {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return UpdateState::None;
+}
+
+Return SnapshotManagerStub::CreateUpdateSnapshots(const DeltaArchiveManifest&) {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return Return::Error();
+}
+
+bool SnapshotManagerStub::MapUpdateSnapshot(const CreateLogicalPartitionParams&, std::string*) {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return false;
+}
+
+bool SnapshotManagerStub::UnmapUpdateSnapshot(const std::string&) {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return false;
+}
+
+bool SnapshotManagerStub::NeedSnapshotsInFirstStageMount() {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return false;
+}
+
+bool SnapshotManagerStub::CreateLogicalAndSnapshotPartitions(const std::string&,
+                                                             const std::chrono::milliseconds&) {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return false;
+}
+
+bool SnapshotManagerStub::HandleImminentDataWipe(const std::function<void()>&) {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return false;
+}
+
+CreateResult SnapshotManagerStub::RecoveryCreateSnapshotDevices() {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return CreateResult::ERROR;
+}
+
+CreateResult SnapshotManagerStub::RecoveryCreateSnapshotDevices(
+        const std::unique_ptr<AutoDevice>&) {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return CreateResult::ERROR;
+}
+
+bool SnapshotManagerStub::Dump(std::ostream&) {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return false;
+}
+
+std::unique_ptr<AutoDevice> SnapshotManagerStub::EnsureMetadataMounted() {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return nullptr;
+}
+
+class SnapshotMergeStatsStub : public ISnapshotMergeStats {
+    bool Start() override { return false; }
+    void set_state(android::snapshot::UpdateState) override {}
+    std::unique_ptr<Result> Finish() override { return nullptr; }
+};
+
+ISnapshotMergeStats* SnapshotManagerStub::GetSnapshotMergeStatsInstance() {
+    static SnapshotMergeStatsStub snapshot_merge_stats;
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return &snapshot_merge_stats;
+}
+
+}  // namespace android::snapshot
diff --git a/fs_mgr/libsnapshot/snapshot_test.cpp b/fs_mgr/libsnapshot/snapshot_test.cpp
index c662838..53a37be 100644
--- a/fs_mgr/libsnapshot/snapshot_test.cpp
+++ b/fs_mgr/libsnapshot/snapshot_test.cpp
@@ -41,6 +41,11 @@
 #include <libsnapshot/test_helpers.h>
 #include "utility.h"
 
+// Mock classes are not used. Header included to ensure mocked class definition aligns with the
+// class itself.
+#include <libsnapshot/mock_device_info.h>
+#include <libsnapshot/mock_snapshot.h>
+
 namespace android {
 namespace snapshot {