diff --git a/dom/fs/test/gtest/parent/TestFileSystemUsageTracking.cpp b/dom/fs/test/gtest/parent/TestFileSystemUsageTracking.cpp
new file mode 100644
index 000000000000..4bd8de3c6aa3
--- /dev/null
+++ b/dom/fs/test/gtest/parent/TestFileSystemUsageTracking.cpp
@@ -0,0 +1,259 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "FileSystemParentTestHelpers.h"
+#include "FileSystemParentTypes.h"
+#include "TestHelpers.h"
+#include "datamodel/FileSystemDataManager.h"
+#include "datamodel/FileSystemDatabaseManager.h"
+#include "gtest/gtest.h"
+#include "mozilla/dom/FileSystemQuotaClientFactory.h"
+#include "mozilla/dom/PFileSystemManager.h"
+#include "mozilla/dom/quota/Client.h"
+#include "mozilla/dom/quota/UsageInfo.h"
+#include "mozilla/dom/quota/test/QuotaManagerDependencyFixture.h"
+
+// This file is intended for integration tests which verify usage tracking
+// without any restart in between.
+
+namespace mozilla::dom::fs::test {
+
+class TestFileSystemUsageTracking
+    : public quota::test::QuotaManagerDependencyFixture {
+ protected:
+  void SetUp() override { ASSERT_NO_FATAL_FAILURE(InitializeFixture()); }
+
+  void TearDown() override {
+    EXPECT_NO_FATAL_FAILURE(ClearStoragesForOrigin(GetTestOriginMetadata()));
+    ASSERT_NO_FATAL_FAILURE(ShutdownFixture());
+  }
+};
+
+TEST_F(TestFileSystemUsageTracking, CheckUsageBeforeAnyFilesOnDisk) {
+  auto backgroundTask = []() {
+    mozilla::Atomic<bool> isCanceled{false};
+    auto ioTask = [&isCanceled](const RefPtr<quota::Client>& quotaClient,
+                                data::FileSystemDatabaseManager* dbm) {
+      ASSERT_FALSE(isCanceled);
+      const quota::OriginMetadata& testOriginMeta = GetTestOriginMetadata();
+      const Origin& testOrigin = testOriginMeta.mOrigin;
+
+      // After initialization,
+      // * database size is not zero
+      // * GetUsageForOrigin and InitOrigin should agree
+      TEST_TRY_UNWRAP(quota::UsageInfo usageNow,
+                      quotaClient->InitOrigin(quota::PERSISTENCE_TYPE_DEFAULT,
+                                              testOriginMeta, isCanceled));
+      ASSERT_NO_FATAL_FAILURE(CheckUsageGreaterThan(usageNow, 0u));
+      const auto initialDbUsage = usageNow.DatabaseUsage().value();
+
+      TEST_TRY_UNWRAP(usageNow, quotaClient->GetUsageForOrigin(
+                                    quota::PERSISTENCE_TYPE_DEFAULT,
+                                    testOriginMeta, isCanceled));
+      ASSERT_NO_FATAL_FAILURE(CheckUsageEqualTo(usageNow, initialDbUsage));
+
+      // Create a new file
+      TEST_TRY_UNWRAP(const EntryId rootId, data::GetRootHandle(testOrigin));
+      FileSystemChildMetadata fileData(rootId, GetTestFileName());
+
+      EntryId testFileId;
+      ASSERT_NO_FATAL_FAILURE(CreateNewEmptyFile(dbm, fileData, testFileId));
+
+      // After a new file has been created (only in the database),
+      // * database size has increased
+      // * GetUsageForOrigin and InitOrigin should agree
+      const auto expectedUse = initialDbUsage + 2 * GetPageSize();
+
+      TEST_TRY_UNWRAP(usageNow, quotaClient->GetUsageForOrigin(
+                                    quota::PERSISTENCE_TYPE_DEFAULT,
+                                    testOriginMeta, isCanceled));
+      ASSERT_NO_FATAL_FAILURE(CheckUsageEqualTo(usageNow, expectedUse));
+
+      TEST_TRY_UNWRAP(usageNow,
+                      quotaClient->InitOrigin(quota::PERSISTENCE_TYPE_DEFAULT,
+                                              testOriginMeta, isCanceled));
+      ASSERT_NO_FATAL_FAILURE(CheckUsageEqualTo(usageNow, expectedUse));
+    };
+
+    RefPtr<mozilla::dom::quota::Client> quotaClient = fs::CreateQuotaClient();
+    ASSERT_TRUE(quotaClient);
+
+    // For uninitialized database, file usage is nothing
+    auto checkTask =
+        [&isCanceled](const RefPtr<mozilla::dom::quota::Client>& quotaClient) {
+          TEST_TRY_UNWRAP(quota::UsageInfo usageNow,
+                          quotaClient->GetUsageForOrigin(
+                              quota::PERSISTENCE_TYPE_DEFAULT,
+                              GetTestOriginMetadata(), isCanceled));
+
+          ASSERT_TRUE(usageNow.DatabaseUsage().isNothing());
+          EXPECT_TRUE(usageNow.FileUsage().isNothing());
+        };
+
+    PerformOnIOThread(std::move(checkTask),
+                      RefPtr<mozilla::dom::quota::Client>{quotaClient});
+
+    // Initialize database
+    Registered<data::FileSystemDataManager> rdm;
+    ASSERT_NO_FATAL_FAILURE(
+        CreateRegisteredDataManager(GetTestOriginMetadata(), rdm));
+
+    // Run tests with an initialized database
+    PerformOnIOThread(std::move(ioTask), std::move(quotaClient),
+                      rdm->MutableDatabaseManagerPtr());
+  };
+
+  PerformOnBackgroundThread(std::move(backgroundTask));
+}
+
+TEST_F(TestFileSystemUsageTracking, WritesToFilesShouldIncreaseUsage) {
+  auto backgroundTask = []() {
+    mozilla::Atomic<bool> isCanceled{false};
+    auto ioTask = [&isCanceled](
+                      const RefPtr<mozilla::dom::quota::Client>& quotaClient,
+                      data::FileSystemDatabaseManager* dbm) {
+      const quota::OriginMetadata& testOriginMeta = GetTestOriginMetadata();
+      const Origin& testOrigin = testOriginMeta.mOrigin;
+
+      TEST_TRY_UNWRAP(const EntryId rootId, data::GetRootHandle(testOrigin));
+      FileSystemChildMetadata fileData(rootId, GetTestFileName());
+
+      EntryId testFileId;
+      ASSERT_NO_FATAL_FAILURE(CreateNewEmptyFile(dbm, fileData, testFileId));
+      // const auto testFileDbUsage = usageNow.DatabaseUsage().value();
+
+      TEST_TRY_UNWRAP(
+          quota::UsageInfo usageNow,
+          quotaClient->GetUsageForOrigin(quota::PERSISTENCE_TYPE_DEFAULT,
+                                         testOriginMeta, isCanceled));
+      ASSERT_TRUE(usageNow.DatabaseUsage().isSome());
+      const auto testFileDbUsage = usageNow.DatabaseUsage().value();
+
+      TEST_TRY_UNWRAP(usageNow,
+                      quotaClient->InitOrigin(quota::PERSISTENCE_TYPE_DEFAULT,
+                                              testOriginMeta, isCanceled));
+      ASSERT_NO_FATAL_FAILURE(CheckUsageEqualTo(usageNow, testFileDbUsage));
+
+      // Fill the file with some content
+      const nsCString& testData = GetTestData();
+
+      ASSERT_NO_FATAL_FAILURE(
+          WriteDataToFile(GetTestOriginMetadata(), dbm, testFileId, testData));
+
+      // In this test we don't lock the file -> no rescan is expected
+      // and InitOrigin should return the previous value
+      TEST_TRY_UNWRAP(usageNow,
+                      quotaClient->InitOrigin(quota::PERSISTENCE_TYPE_DEFAULT,
+                                              testOriginMeta, isCanceled));
+      ASSERT_NO_FATAL_FAILURE(CheckUsageEqualTo(usageNow, testFileDbUsage));
+
+      // When data manager unlocks the file, it should call update
+      // but in this test we call it directly
+      ASSERT_NSEQ(NS_OK, dbm->UpdateUsage(FileId(testFileId)));
+
+      const auto expectedTotalUsage = testFileDbUsage + testData.Length();
+
+      // Disk usage should have increased after writing
+      TEST_TRY_UNWRAP(usageNow,
+                      quotaClient->InitOrigin(quota::PERSISTENCE_TYPE_DEFAULT,
+                                              testOriginMeta, isCanceled));
+      ASSERT_NO_FATAL_FAILURE(CheckUsageEqualTo(usageNow, expectedTotalUsage));
+
+      // The usage values should now agree
+      TEST_TRY_UNWRAP(usageNow, quotaClient->GetUsageForOrigin(
+                                    quota::PERSISTENCE_TYPE_DEFAULT,
+                                    testOriginMeta, isCanceled));
+      ASSERT_NO_FATAL_FAILURE(CheckUsageEqualTo(usageNow, expectedTotalUsage));
+    };
+
+    RefPtr<mozilla::dom::quota::Client> quotaClient = fs::CreateQuotaClient();
+    ASSERT_TRUE(quotaClient);
+
+    // Initialize database
+    Registered<data::FileSystemDataManager> rdm;
+    ASSERT_NO_FATAL_FAILURE(
+        CreateRegisteredDataManager(GetTestOriginMetadata(), rdm));
+
+    // Run tests with an initialized database
+    PerformOnIOThread(std::move(ioTask), std::move(quotaClient),
+                      rdm->MutableDatabaseManagerPtr());
+  };
+
+  PerformOnBackgroundThread(std::move(backgroundTask));
+}
+
+TEST_F(TestFileSystemUsageTracking, RemovingFileShouldDecreaseUsage) {
+  auto backgroundTask = []() {
+    mozilla::Atomic<bool> isCanceled{false};
+    auto ioTask = [&isCanceled](
+                      const RefPtr<mozilla::dom::quota::Client>& quotaClient,
+                      data::FileSystemDatabaseManager* dbm) {
+      const quota::OriginMetadata& testOriginMeta = GetTestOriginMetadata();
+      const Origin& testOrigin = testOriginMeta.mOrigin;
+
+      TEST_TRY_UNWRAP(const EntryId rootId, data::GetRootHandle(testOrigin));
+      FileSystemChildMetadata fileData(rootId, GetTestFileName());
+
+      EntryId testFileId;
+      ASSERT_NO_FATAL_FAILURE(CreateNewEmptyFile(dbm, fileData, testFileId));
+      TEST_TRY_UNWRAP(quota::UsageInfo usageNow,
+                      quotaClient->InitOrigin(quota::PERSISTENCE_TYPE_DEFAULT,
+                                              testOriginMeta, isCanceled));
+      ASSERT_TRUE(usageNow.DatabaseUsage().isSome());
+      const auto testFileDbUsage = usageNow.DatabaseUsage().value();
+
+      // Fill the file with some content
+      const nsCString& testData = GetTestData();
+      const auto expectedTotalUsage = testFileDbUsage + testData.Length();
+
+      ASSERT_NO_FATAL_FAILURE(
+          WriteDataToFile(GetTestOriginMetadata(), dbm, testFileId, testData));
+
+      // Currently, usage is expected to be updated on unlock by data manager
+      // but here UpdateUsage() is called directly
+      ASSERT_NSEQ(NS_OK, dbm->UpdateUsage(FileId(testFileId)));
+
+      // At least some file disk usage should have appeared after unlocking
+      TEST_TRY_UNWRAP(usageNow, quotaClient->GetUsageForOrigin(
+                                    quota::PERSISTENCE_TYPE_DEFAULT,
+                                    testOriginMeta, isCanceled));
+      ASSERT_NO_FATAL_FAILURE(CheckUsageEqualTo(usageNow, expectedTotalUsage));
+
+      TEST_TRY_UNWRAP(bool wasRemoved,
+                      dbm->RemoveFile({rootId, GetTestFileName()}));
+      ASSERT_TRUE(wasRemoved);
+
+      // Removes cascade and usage table should be up to date immediately
+      TEST_TRY_UNWRAP(usageNow,
+                      quotaClient->InitOrigin(quota::PERSISTENCE_TYPE_DEFAULT,
+                                              testOriginMeta, isCanceled));
+      ASSERT_NO_FATAL_FAILURE(CheckUsageEqualTo(usageNow, testFileDbUsage));
+
+      // GetUsageForOrigin should agree
+      TEST_TRY_UNWRAP(usageNow, quotaClient->GetUsageForOrigin(
+                                    quota::PERSISTENCE_TYPE_DEFAULT,
+                                    testOriginMeta, isCanceled));
+
+      ASSERT_NO_FATAL_FAILURE(CheckUsageEqualTo(usageNow, testFileDbUsage));
+    };
+
+    RefPtr<mozilla::dom::quota::Client> quotaClient = fs::CreateQuotaClient();
+    ASSERT_TRUE(quotaClient);
+
+    // Initialize database
+    Registered<data::FileSystemDataManager> rdm;
+    ASSERT_NO_FATAL_FAILURE(
+        CreateRegisteredDataManager(GetTestOriginMetadata(), rdm));
+
+    // Run tests with an initialized database
+    PerformOnIOThread(std::move(ioTask), std::move(quotaClient),
+                      rdm->MutableDatabaseManagerPtr());
+  };
+
+  PerformOnBackgroundThread(std::move(backgroundTask));
+}
+
+}  // namespace mozilla::dom::fs::test
diff --git a/dom/fs/test/gtest/parent/moz.build b/dom/fs/test/gtest/parent/moz.build
index 13c3bd3b8c0b..6f4aeb2fe62c 100644
--- a/dom/fs/test/gtest/parent/moz.build
+++ b/dom/fs/test/gtest/parent/moz.build
@@ -10,6 +10,7 @@ UNIFIED_SOURCES = [
     "FileSystemParentTestHelpers.cpp",
     "TestFileSystemHashSource.cpp",
     "TestFileSystemQuotaClient.cpp",
+    "TestFileSystemUsageTracking.cpp",
 ]
 
 include("/ipc/chromium/chromium-config.mozbuild")