diff --git a/packages/element-web-module-api/package.json b/packages/element-web-module-api/package.json
index c3b8093a61..2c7f17038a 100644
--- a/packages/element-web-module-api/package.json
+++ b/packages/element-web-module-api/package.json
@@ -19,7 +19,8 @@
     ],
     "scripts": {
         "prepare": "vite build && api-extractor run",
-        "lint:ts": "tsc --noEmit"
+        "lint:ts": "tsc --noEmit",
+        "test": "vitest"
     },
     "devDependencies": {
         "@matrix-org/react-sdk-module-api": "^2.5.0",
@@ -27,11 +28,14 @@
         "@types/node": "^22.10.7",
         "@types/react": "^18",
         "@types/semver": "^7.5.8",
+        "@vitest/coverage-v8": "^3.0.4",
         "matrix-web-i18n": "^3.3.0",
         "semver": "^7.6.3",
         "typescript": "^5.7.3",
         "vite": "^6.0.11",
-        "vite-plugin-dts": "^4.5.0"
+        "vite-plugin-dts": "^4.5.0",
+        "vitest": "^3.0.4",
+        "vitest-sonar-reporter": "^2.0.0"
     },
     "peerDependencies": {
         "@matrix-org/react-sdk-module-api": "*",
diff --git a/packages/element-web-module-api/src/api.test.ts b/packages/element-web-module-api/src/api.test.ts
new file mode 100644
index 0000000000..62dd3973aa
--- /dev/null
+++ b/packages/element-web-module-api/src/api.test.ts
@@ -0,0 +1,23 @@
+/*
+Copyright 2025 New Vector Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE files in the repository root for full details.
+*/
+
+import { expect, test } from "vitest";
+
+import { Api } from ".";
+import { isModule } from "./api.js";
+
+const TestModule = {
+    default: class TestModule {
+        public static moduleApiVersion = "1.0.0";
+        public constructor(private readonly api: Api) {}
+        public async load(): Promise<void> {}
+    },
+};
+
+test("isModule correctly identifies valid modules", () => {
+    expect(isModule(TestModule)).toBe(true);
+});
diff --git a/packages/element-web-module-api/src/api.ts b/packages/element-web-module-api/src/api.ts
index 1ab56aadd4..5534411375 100644
--- a/packages/element-web-module-api/src/api.ts
+++ b/packages/element-web-module-api/src/api.ts
@@ -40,13 +40,13 @@ export interface ModuleExport {
 }
 
 const moduleExportSignature: Record<keyof ModuleExport, Type> = {
-    default: "object",
+    default: "function",
 };
 
 type Type = "function" | "string" | "number" | "boolean" | "object";
 
-function isInterface<T>(obj: unknown, keys: Record<keyof T, Type>): obj is T {
-    if (obj === null || typeof obj !== "object") return false;
+function isInterface<T>(obj: unknown, type: "object" | "function", keys: Record<keyof T, Type>): obj is T {
+    if (obj === null || typeof obj !== type) return false;
     for (const key in keys) {
         if (typeof (obj as Record<keyof T, unknown>)[key] !== keys[key]) return false;
     }
@@ -55,9 +55,9 @@ function isInterface<T>(obj: unknown, keys: Record<keyof T, Type>): obj is T {
 
 export function isModule(module: unknown): module is ModuleExport {
     return (
-        isInterface(module, moduleExportSignature) &&
-        isInterface(module.default, moduleFactorySignature) &&
-        isInterface(module.default.prototype, moduleSignature)
+        isInterface(module, "object", moduleExportSignature) &&
+        isInterface(module.default, "function", moduleFactorySignature) &&
+        isInterface(module.default.prototype, "object", moduleSignature)
     );
 }
 
diff --git a/packages/element-web-module-api/src/loader.spec.ts b/packages/element-web-module-api/src/loader.spec.ts
new file mode 100644
index 0000000000..853b6d3eb6
--- /dev/null
+++ b/packages/element-web-module-api/src/loader.spec.ts
@@ -0,0 +1,58 @@
+/*
+Copyright 2025 New Vector Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE files in the repository root for full details.
+*/
+
+import { expect, test, describe, vi, beforeEach } from "vitest";
+
+import { Api, ModuleIncompatibleError, ModuleLoader } from ".";
+
+describe("ModuleIncompatibleError", () => {
+    test("should extend Error", () => {
+        expect(new ModuleIncompatibleError("1.0.0")).toBeInstanceOf(Error);
+    });
+});
+
+describe("ModuleLoader", () => {
+    const mockApi = {} as Api;
+
+    beforeEach(() => {
+        vi.stubGlobal("__VERSION__", "1.0.1");
+    });
+
+    test("should load a module", async () => {
+        const TestModule = {
+            default: class TestModule {
+                public static moduleApiVersion = "^1.0.0";
+                public constructor(private readonly api: Api) {}
+                public async load(): Promise<void> {}
+            },
+        };
+
+        const spy = vi.spyOn(TestModule.default.prototype, "load");
+
+        const loader = new ModuleLoader(mockApi);
+        await loader.load(TestModule);
+        await loader.start();
+        expect(spy).toHaveBeenCalledWith();
+    });
+
+    test("should fail to load an incompatible module", async () => {
+        const TestModule = {
+            default: class TestModule {
+                public static moduleApiVersion = "^2";
+                public constructor(private readonly api: Api) {}
+                public async load(): Promise<void> {}
+            },
+        };
+
+        const spy = vi.spyOn(TestModule.default.prototype, "load");
+
+        const loader = new ModuleLoader(mockApi);
+        await expect(loader.load(TestModule)).rejects.toThrowError(ModuleIncompatibleError);
+        await loader.start();
+        expect(spy).not.toHaveBeenCalledWith();
+    });
+});
diff --git a/packages/element-web-module-api/vite.config.ts b/packages/element-web-module-api/vite.config.ts
index 0fee8e9834..6b0d47a8a2 100644
--- a/packages/element-web-module-api/vite.config.ts
+++ b/packages/element-web-module-api/vite.config.ts
@@ -27,4 +27,22 @@ export default defineConfig({
     define: {
         __VERSION__: JSON.stringify(process.env.npm_package_version),
     },
+    test: {
+        coverage: {
+            provider: "v8",
+            include: ["src/**/*"],
+            reporter: "lcov",
+        },
+        reporters: [
+            [
+                "vitest-sonar-reporter",
+                {
+                    outputFile: "coverage/sonar-report.xml",
+                    onWritePath(path: string): string {
+                        return `packages/element-web-module-api/${path}`;
+                    },
+                },
+            ],
+        ],
+    },
 });