diff --git a/lib/overlay-database-utils.test.js b/lib/overlay-database-utils.test.js
new file mode 100644
index 000000000..4daf830cd
--- /dev/null
+++ b/lib/overlay-database-utils.test.js
@@ -0,0 +1,94 @@
+"use strict";
+var __createBinding = (this && this.__createBinding) || (Object.create ? (function(o, m, k, k2) {
+    if (k2 === undefined) k2 = k;
+    var desc = Object.getOwnPropertyDescriptor(m, k);
+    if (!desc || ("get" in desc ? !m.__esModule : desc.writable || desc.configurable)) {
+      desc = { enumerable: true, get: function() { return m[k]; } };
+    }
+    Object.defineProperty(o, k2, desc);
+}) : (function(o, m, k, k2) {
+    if (k2 === undefined) k2 = k;
+    o[k2] = m[k];
+}));
+var __setModuleDefault = (this && this.__setModuleDefault) || (Object.create ? (function(o, v) {
+    Object.defineProperty(o, "default", { enumerable: true, value: v });
+}) : function(o, v) {
+    o["default"] = v;
+});
+var __importStar = (this && this.__importStar) || (function () {
+    var ownKeys = function(o) {
+        ownKeys = Object.getOwnPropertyNames || function (o) {
+            var ar = [];
+            for (var k in o) if (Object.prototype.hasOwnProperty.call(o, k)) ar[ar.length] = k;
+            return ar;
+        };
+        return ownKeys(o);
+    };
+    return function (mod) {
+        if (mod && mod.__esModule) return mod;
+        var result = {};
+        if (mod != null) for (var k = ownKeys(mod), i = 0; i < k.length; i++) if (k[i] !== "default") __createBinding(result, mod, k[i]);
+        __setModuleDefault(result, mod);
+        return result;
+    };
+})();
+var __importDefault = (this && this.__importDefault) || function (mod) {
+    return (mod && mod.__esModule) ? mod : { "default": mod };
+};
+Object.defineProperty(exports, "__esModule", { value: true });
+const fs = __importStar(require("fs"));
+const path = __importStar(require("path"));
+const ava_1 = __importDefault(require("ava"));
+const sinon = __importStar(require("sinon"));
+const actionsUtil = __importStar(require("./actions-util"));
+const gitUtils = __importStar(require("./git-utils"));
+const logging_1 = require("./logging");
+const overlay_database_utils_1 = require("./overlay-database-utils");
+const testing_utils_1 = require("./testing-utils");
+const util_1 = require("./util");
+(0, testing_utils_1.setupTests)(ava_1.default);
+(0, ava_1.default)("writeOverlayChangesFile generates correct changes file", async (t) => {
+    await (0, util_1.withTmpDir)(async (tmpDir) => {
+        const dbLocation = path.join(tmpDir, "db");
+        await fs.promises.mkdir(dbLocation, { recursive: true });
+        const sourceRoot = path.join(tmpDir, "src");
+        await fs.promises.mkdir(sourceRoot, { recursive: true });
+        const tempDir = path.join(tmpDir, "temp");
+        await fs.promises.mkdir(tempDir, { recursive: true });
+        const logger = (0, logging_1.getRunnerLogger)(true);
+        const config = (0, testing_utils_1.createTestConfig)({ dbLocation });
+        // Mock the getFileOidsUnderPath function to return base OIDs
+        const baseOids = {
+            "unchanged.js": "aaa111",
+            "modified.js": "bbb222",
+            "deleted.js": "ccc333",
+        };
+        const getFileOidsStubForBase = sinon
+            .stub(gitUtils, "getFileOidsUnderPath")
+            .resolves(baseOids);
+        // Write the base database OIDs file
+        await (0, overlay_database_utils_1.writeBaseDatabaseOidsFile)(config, sourceRoot);
+        getFileOidsStubForBase.restore();
+        // Mock the getFileOidsUnderPath function to return overlay OIDs
+        const currentOids = {
+            "unchanged.js": "aaa111",
+            "modified.js": "ddd444", // Changed OID
+            "added.js": "eee555", // New file
+        };
+        const getFileOidsStubForOverlay = sinon
+            .stub(gitUtils, "getFileOidsUnderPath")
+            .resolves(currentOids);
+        // Write the overlay changes file, which uses the mocked overlay OIDs
+        // and the base database OIDs file
+        const getTempDirStub = sinon
+            .stub(actionsUtil, "getTemporaryDirectory")
+            .returns(tempDir);
+        const changesFilePath = await (0, overlay_database_utils_1.writeOverlayChangesFile)(config, sourceRoot, logger);
+        getFileOidsStubForOverlay.restore();
+        getTempDirStub.restore();
+        const fileContent = await fs.promises.readFile(changesFilePath, "utf-8");
+        const parsedContent = JSON.parse(fileContent);
+        t.deepEqual(parsedContent.changes.sort(), ["added.js", "deleted.js", "modified.js"], "Should identify added, deleted, and modified files");
+    });
+});
+//# sourceMappingURL=overlay-database-utils.test.js.map
\ No newline at end of file
diff --git a/lib/overlay-database-utils.test.js.map b/lib/overlay-database-utils.test.js.map
new file mode 100644
index 000000000..1d58d93ee
--- /dev/null
+++ b/lib/overlay-database-utils.test.js.map
@@ -0,0 +1 @@
+{"version":3,"file":"overlay-database-utils.test.js","sourceRoot":"","sources":["../src/overlay-database-utils.test.ts"],"names":[],"mappings":";;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;AAAA,uCAAyB;AACzB,2CAA6B;AAE7B,8CAAuB;AACvB,6CAA+B;AAE/B,4DAA8C;AAC9C,sDAAwC;AACxC,uCAA4C;AAC5C,qEAGkC;AAClC,mDAA+D;AAC/D,iCAAoC;AAEpC,IAAA,0BAAU,EAAC,aAAI,CAAC,CAAC;AAEjB,IAAA,aAAI,EAAC,wDAAwD,EAAE,KAAK,EAAE,CAAC,EAAE,EAAE;IACzE,MAAM,IAAA,iBAAU,EAAC,KAAK,EAAE,MAAM,EAAE,EAAE;QAChC,MAAM,UAAU,GAAG,IAAI,CAAC,IAAI,CAAC,MAAM,EAAE,IAAI,CAAC,CAAC;QAC3C,MAAM,EAAE,CAAC,QAAQ,CAAC,KAAK,CAAC,UAAU,EAAE,EAAE,SAAS,EAAE,IAAI,EAAE,CAAC,CAAC;QACzD,MAAM,UAAU,GAAG,IAAI,CAAC,IAAI,CAAC,MAAM,EAAE,KAAK,CAAC,CAAC;QAC5C,MAAM,EAAE,CAAC,QAAQ,CAAC,KAAK,CAAC,UAAU,EAAE,EAAE,SAAS,EAAE,IAAI,EAAE,CAAC,CAAC;QACzD,MAAM,OAAO,GAAG,IAAI,CAAC,IAAI,CAAC,MAAM,EAAE,MAAM,CAAC,CAAC;QAC1C,MAAM,EAAE,CAAC,QAAQ,CAAC,KAAK,CAAC,OAAO,EAAE,EAAE,SAAS,EAAE,IAAI,EAAE,CAAC,CAAC;QAEtD,MAAM,MAAM,GAAG,IAAA,yBAAe,EAAC,IAAI,CAAC,CAAC;QACrC,MAAM,MAAM,GAAG,IAAA,gCAAgB,EAAC,EAAE,UAAU,EAAE,CAAC,CAAC;QAEhD,6DAA6D;QAC7D,MAAM,QAAQ,GAAG;YACf,cAAc,EAAE,QAAQ;YACxB,aAAa,EAAE,QAAQ;YACvB,YAAY,EAAE,QAAQ;SACvB,CAAC;QACF,MAAM,sBAAsB,GAAG,KAAK;aACjC,IAAI,CAAC,QAAQ,EAAE,sBAAsB,CAAC;aACtC,QAAQ,CAAC,QAAQ,CAAC,CAAC;QAEtB,oCAAoC;QACpC,MAAM,IAAA,kDAAyB,EAAC,MAAM,EAAE,UAAU,CAAC,CAAC;QACpD,sBAAsB,CAAC,OAAO,EAAE,CAAC;QAEjC,gEAAgE;QAChE,MAAM,WAAW,GAAG;YAClB,cAAc,EAAE,QAAQ;YACxB,aAAa,EAAE,QAAQ,EAAE,cAAc;YACvC,UAAU,EAAE,QAAQ,EAAE,WAAW;SAClC,CAAC;QACF,MAAM,yBAAyB,GAAG,KAAK;aACpC,IAAI,CAAC,QAAQ,EAAE,sBAAsB,CAAC;aACtC,QAAQ,CAAC,WAAW,CAAC,CAAC;QAEzB,qEAAqE;QACrE,kCAAkC;QAClC,MAAM,cAAc,GAAG,KAAK;aACzB,IAAI,CAAC,WAAW,EAAE,uBAAuB,CAAC;aAC1C,OAAO,CAAC,OAAO,CAAC,CAAC;QACpB,MAAM,eAAe,GAAG,MAAM,IAAA,gDAAuB,EACnD,MAAM,EACN,UAAU,EACV,MAAM,CACP,CAAC;QACF,yBAAyB,CAAC,OAAO,EAAE,CAAC;QACpC,cAAc,CAAC,OAAO,EAAE,CAAC;QAEzB,MAAM,WAAW,GAAG,MAAM,EAAE,CAAC,QAAQ,CAAC,QAAQ,CAAC,eAAe,EAAE,OAAO,CAAC,CAAC;QACzE,MAAM,aAAa,GAAG,IAAI,CAAC,KAAK,CAAC,WAAW,CAA0B,CAAC;QAEvE,CAAC,CAAC,SAAS,CACT,aAAa,CAAC,OAAO,CAAC,IAAI,EAAE,EAC5B,CAAC,UAAU,EAAE,YAAY,EAAE,aAAa,CAAC,EACzC,oDAAoD,CACrD,CAAC;IACJ,CAAC,CAAC,CAAC;AACL,CAAC,CAAC,CAAC"}
\ No newline at end of file
diff --git a/src/overlay-database-utils.test.ts b/src/overlay-database-utils.test.ts
new file mode 100644
index 000000000..3b2027975
--- /dev/null
+++ b/src/overlay-database-utils.test.ts
@@ -0,0 +1,77 @@
+import * as fs from "fs";
+import * as path from "path";
+
+import test from "ava";
+import * as sinon from "sinon";
+
+import * as actionsUtil from "./actions-util";
+import * as gitUtils from "./git-utils";
+import { getRunnerLogger } from "./logging";
+import {
+  writeBaseDatabaseOidsFile,
+  writeOverlayChangesFile,
+} from "./overlay-database-utils";
+import { createTestConfig, setupTests } from "./testing-utils";
+import { withTmpDir } from "./util";
+
+setupTests(test);
+
+test("writeOverlayChangesFile generates correct changes file", async (t) => {
+  await withTmpDir(async (tmpDir) => {
+    const dbLocation = path.join(tmpDir, "db");
+    await fs.promises.mkdir(dbLocation, { recursive: true });
+    const sourceRoot = path.join(tmpDir, "src");
+    await fs.promises.mkdir(sourceRoot, { recursive: true });
+    const tempDir = path.join(tmpDir, "temp");
+    await fs.promises.mkdir(tempDir, { recursive: true });
+
+    const logger = getRunnerLogger(true);
+    const config = createTestConfig({ dbLocation });
+
+    // Mock the getFileOidsUnderPath function to return base OIDs
+    const baseOids = {
+      "unchanged.js": "aaa111",
+      "modified.js": "bbb222",
+      "deleted.js": "ccc333",
+    };
+    const getFileOidsStubForBase = sinon
+      .stub(gitUtils, "getFileOidsUnderPath")
+      .resolves(baseOids);
+
+    // Write the base database OIDs file
+    await writeBaseDatabaseOidsFile(config, sourceRoot);
+    getFileOidsStubForBase.restore();
+
+    // Mock the getFileOidsUnderPath function to return overlay OIDs
+    const currentOids = {
+      "unchanged.js": "aaa111",
+      "modified.js": "ddd444", // Changed OID
+      "added.js": "eee555", // New file
+    };
+    const getFileOidsStubForOverlay = sinon
+      .stub(gitUtils, "getFileOidsUnderPath")
+      .resolves(currentOids);
+
+    // Write the overlay changes file, which uses the mocked overlay OIDs
+    // and the base database OIDs file
+    const getTempDirStub = sinon
+      .stub(actionsUtil, "getTemporaryDirectory")
+      .returns(tempDir);
+    const changesFilePath = await writeOverlayChangesFile(
+      config,
+      sourceRoot,
+      logger,
+    );
+    getFileOidsStubForOverlay.restore();
+    getTempDirStub.restore();
+
+    const fileContent = await fs.promises.readFile(changesFilePath, "utf-8");
+    const parsedContent = JSON.parse(fileContent) as { changes: string[] };
+
+    t.deepEqual(
+      parsedContent.changes.sort(),
+      ["added.js", "deleted.js", "modified.js"],
+      "Should identify added, deleted, and modified files",
+    );
+  });
+});