From e2de6bf47523855e4f6dbcf1ee9552dc09ae712f Mon Sep 17 00:00:00 2001
From: Abhishek Chatterjee <abhishekchatterjeejit@gmail.com>
Date: Mon, 18 May 2026 18:14:48 +0530
Subject: [PATCH 1/3] feat(email): ROSS-168: implement configurable email
 plugin with dummy engine support

---
 example_config.json             |  3 ++
 src/interfaces/config.ts        |  6 +++
 src/plugin/email.ts             | 24 +++++++++
 src/server.ts                   |  6 +++
 src/types/fastify.d.ts          |  7 +++
 src/validators/config/schema.ts | 13 +++++
 tests/plugin/email.test.ts      | 86 +++++++++++++++++++++++++++++++++
 tests/server.test.ts            | 28 +++++++++++
 tests/validators/config.test.ts | 52 ++++++++++++++++++++
 9 files changed, 225 insertions(+)
 create mode 100644 src/plugin/email.ts
 create mode 100644 tests/plugin/email.test.ts

diff --git a/example_config.json b/example_config.json
index 8839f11..b5de3ef 100644
--- a/example_config.json
+++ b/example_config.json
@@ -52,6 +52,9 @@
             "passwordColumn": "password"
         }
     },
+    "email": {
+        "emailEngine": "dummy"
+    },
     "models": [
         {
             "name": "users",
diff --git a/src/interfaces/config.ts b/src/interfaces/config.ts
index c7f4031..f4b9942 100644
--- a/src/interfaces/config.ts
+++ b/src/interfaces/config.ts
@@ -60,6 +60,7 @@ export type JsonSchemaObject = {
 export type WebhookData = 'query' | 'body' | 'params' | 'resp';
 export type AuthEngine = 'api-key' | 'up-auth';
 export type SspParamType = 'path' | 'query' | 'body';
+export type EmailEngine = 'dummy';
 
 export interface SwaggerConfig {
   enabled: boolean;
@@ -211,6 +212,10 @@ export interface AuthConfig {
   apiKey?: string;
 }
 
+export interface EmailConfig {
+  emailEngine: EmailEngine;
+}
+
 export interface AppConfig {
   application: ApplicationConfig;
   swagger: SwaggerConfig;
@@ -220,4 +225,5 @@ export interface AppConfig {
   cache_db?: CacheDbConfig;
   customAPIs?: CustomAPIConfig;
   auth?: AuthConfig;
+  email?: EmailConfig;
 }
diff --git a/src/plugin/email.ts b/src/plugin/email.ts
new file mode 100644
index 0000000..94be8df
--- /dev/null
+++ b/src/plugin/email.ts
@@ -0,0 +1,24 @@
+import {FastifyInstance} from 'fastify';
+import fp from 'fastify-plugin';
+
+const sendDummyEmail = async (
+  email: string,
+  htmlBody: string,
+  body: string,
+) => {
+  console.log('Email:', email);
+  console.log('HTML Body:', htmlBody);
+  console.log('Body:', body);
+};
+
+export default fp(async (fastify: FastifyInstance) => {
+  const communicate = {
+    sendEmail: async (email: string, htmlBody: string, body: string) => {
+      if (fastify.appConfig.email.emailEngine === 'dummy') {
+        await sendDummyEmail(email, htmlBody, body);
+      }
+    },
+  };
+
+  fastify.decorate('communicate', communicate);
+});
diff --git a/src/server.ts b/src/server.ts
index 51e884b..7f86a63 100644
--- a/src/server.ts
+++ b/src/server.ts
@@ -11,6 +11,7 @@ import migrateDatabase from '@/migrator';
 import authPlugin from '@/plugin/auth';
 import cachePlugin from '@/plugin/cache';
 import dbPlugin from '@/plugin/database';
+import emailPlugin from '@/plugin/email';
 import rateLimitPlugin from '@/plugin/rate-limit';
 import responsePlugin from '@/plugin/response';
 import sspPlugin from '@/plugin/ssp';
@@ -121,6 +122,11 @@ export async function startServer(
   // config-driven cache (Redis or NodeCache)
   await app.register(cachePlugin);
 
+  // config-driven email
+  if (config.email) {
+    await app.register(emailPlugin);
+  }
+
   // config-driven rate limit
   if (config.application.rateLimit) {
     await app.register(rateLimitPlugin, {
diff --git a/src/types/fastify.d.ts b/src/types/fastify.d.ts
index 3667ee1..776b8bd 100644
--- a/src/types/fastify.d.ts
+++ b/src/types/fastify.d.ts
@@ -34,5 +34,12 @@ declare module 'fastify' {
       payload: unknown,
     ) => Promise<void>;
     enforceSSP: (request: import('fastify').FastifyRequest) => void;
+    communicate: {
+      sendEmail: (
+        email: string,
+        htmlBody: string,
+        body: string,
+      ) => Promise<void>;
+    };
   }
 }
diff --git a/src/validators/config/schema.ts b/src/validators/config/schema.ts
index ef1395a..d282f75 100644
--- a/src/validators/config/schema.ts
+++ b/src/validators/config/schema.ts
@@ -462,6 +462,18 @@ const authSchema = {
   },
 };
 
+const emailSchema = {
+  type: 'object',
+  additionalProperties: false,
+  required: ['emailEngine'],
+  properties: {
+    emailEngine: {
+      type: 'string',
+      enum: ['dummy'],
+    },
+  },
+};
+
 const schema = {
   type: 'object',
   required: ['application', 'swagger', 'database', 'models'],
@@ -479,6 +491,7 @@ const schema = {
     cache_db: cacheDbSchema,
     customAPIs: customAPIsSchema,
     auth: authSchema,
+    email: emailSchema,
   },
 };
 
diff --git a/tests/plugin/email.test.ts b/tests/plugin/email.test.ts
new file mode 100644
index 0000000..de75576
--- /dev/null
+++ b/tests/plugin/email.test.ts
@@ -0,0 +1,86 @@
+import Fastify, {FastifyInstance} from 'fastify';
+import {afterEach, beforeEach, describe, expect, it, vi} from 'vitest';
+
+import emailPlugin from '@/plugin/email';
+
+import {AppConfig} from '@/interfaces/config';
+
+describe('email plugin', () => {
+  let app: FastifyInstance;
+
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  afterEach(async () => {
+    if (app) {
+      await app.close();
+    }
+  });
+
+  it('decorates fastify with communicate', async () => {
+    app = Fastify();
+    app.appConfig = {
+      email: {
+        emailEngine: 'dummy',
+      },
+    } as unknown as AppConfig;
+
+    await app.register(emailPlugin);
+    await app.ready();
+
+    expect(app.hasDecorator('communicate')).toBe(true);
+    expect(app.communicate).toBeDefined();
+    expect(typeof app.communicate.sendEmail).toBe('function');
+  });
+
+  it('sends a dummy email when emailEngine is dummy', async () => {
+    app = Fastify();
+    app.appConfig = {
+      email: {
+        emailEngine: 'dummy',
+      },
+    } as unknown as AppConfig;
+
+    await app.register(emailPlugin);
+    await app.ready();
+
+    const consoleLogSpy = vi.spyOn(console, 'log').mockImplementation(() => {});
+
+    await app.communicate.sendEmail(
+      'test@example.com',
+      '<h1>Hello</h1>',
+      'Hello',
+    );
+
+    expect(consoleLogSpy).toHaveBeenCalledWith('Email:', 'test@example.com');
+    expect(consoleLogSpy).toHaveBeenCalledWith('HTML Body:', '<h1>Hello</h1>');
+    expect(consoleLogSpy).toHaveBeenCalledWith('Body:', 'Hello');
+
+    consoleLogSpy.mockRestore();
+  });
+
+  it('does not send an email if emailEngine is not dummy', async () => {
+    app = Fastify();
+    app.appConfig = {
+      email: {
+        emailEngine: 'other' as unknown as 'dummy',
+      },
+    } as unknown as AppConfig;
+
+    await app.register(emailPlugin);
+    await app.ready();
+
+    const consoleLogSpy = vi.spyOn(console, 'log').mockImplementation(() => {});
+
+    await app.communicate.sendEmail(
+      'test@example.com',
+      '<h1>Hello</h1>',
+      'Hello',
+    );
+
+    expect(consoleLogSpy).not.toHaveBeenCalled();
+
+    consoleLogSpy.mockRestore();
+  });
+});
diff --git a/tests/server.test.ts b/tests/server.test.ts
index 5e90596..ee83493 100644
--- a/tests/server.test.ts
+++ b/tests/server.test.ts
@@ -7,6 +7,7 @@ import Fastify, {
 import {afterEach, beforeEach, describe, expect, it, vi} from 'vitest';
 
 import migrateDatabase from '@/migrator/index';
+import emailPlugin from '@/plugin/email';
 import {startServer} from '@/server';
 
 import {registerRoutes} from '@/routes/index';
@@ -542,4 +543,31 @@ describe('Server', () => {
       ).toHaveProperty('apiKeyAuth');
     });
   });
+
+  describe('Email Configuration', () => {
+    it('should register email plugin when email is configured', async () => {
+      const configWithEmail: AppConfig = {
+        ...mockConfig,
+        email: {
+          emailEngine: 'dummy',
+        },
+      };
+
+      const registerMock = mockApp.register;
+      await startServer(configWithEmail, 3000, 'dev');
+
+      expect(registerMock).toHaveBeenCalledWith(emailPlugin);
+    });
+
+    it('should not register email plugin when email is not configured', async () => {
+      const registerMock = mockApp.register;
+      await startServer(mockConfig, 3000, 'dev');
+
+      // Assert that none of the registered calls are the emailPlugin
+      const emailPluginCall = registerMock.mock.calls.find(
+        (call: unknown[]) => call[0] === emailPlugin,
+      );
+      expect(emailPluginCall).toBeUndefined();
+    });
+  });
 });
diff --git a/tests/validators/config.test.ts b/tests/validators/config.test.ts
index a92cad9..5b54696 100644
--- a/tests/validators/config.test.ts
+++ b/tests/validators/config.test.ts
@@ -3466,3 +3466,55 @@ describe('validateValidAuthorizationConfig', () => {
     expect(validateConfig(config as unknown as AppConfig)).toEqual(config);
   });
 });
+
+// check email configs validation
+describe('validateEmailConfig', () => {
+  it('should pass when email config is valid', () => {
+    const config = {
+      ...validBaseConfig,
+      email: {
+        emailEngine: 'dummy',
+      },
+    };
+
+    expect(validateConfig(config as unknown as AppConfig)).toEqual(config);
+  });
+
+  it('should throw when email config is missing required emailEngine', () => {
+    const config = {
+      ...validBaseConfig,
+      email: {},
+    };
+
+    expect(() => validateConfig(config as unknown as AppConfig)).toThrow(
+      "must have required property 'emailEngine'",
+    );
+  });
+
+  it('should throw when email config has invalid emailEngine enum value', () => {
+    const config = {
+      ...validBaseConfig,
+      email: {
+        emailEngine: 'invalid-engine',
+      },
+    };
+
+    expect(() => validateConfig(config as unknown as AppConfig)).toThrow(
+      'must be equal to one of the allowed values',
+    );
+  });
+
+  it('should throw when email config has extra properties', () => {
+    const config = {
+      ...validBaseConfig,
+      email: {
+        emailEngine: 'dummy',
+        extraProperty: true,
+      },
+    };
+
+    expect(() => validateConfig(config as unknown as AppConfig)).toThrow(
+      'must NOT have additional properties',
+    );
+  });
+});

From b07c41e611cfb4a08cd7360c852b1eb25f7b072e Mon Sep 17 00:00:00 2001
From: Abhishek Chatterjee <abhishekchatterjeejit@gmail.com>
Date: Mon, 18 May 2026 18:16:11 +0530
Subject: [PATCH 2/3] refactor(email): ROSS-168: rename email plugin to
 communicate to support broader messaging functionality

---
 src/plugin/{email.ts => communicate.ts}             | 0
 src/server.ts                                       | 2 +-
 tests/plugin/{email.test.ts => communicate.test.ts} | 2 +-
 tests/server.test.ts                                | 2 +-
 4 files changed, 3 insertions(+), 3 deletions(-)
 rename src/plugin/{email.ts => communicate.ts} (100%)
 rename tests/plugin/{email.test.ts => communicate.test.ts} (97%)

diff --git a/src/plugin/email.ts b/src/plugin/communicate.ts
similarity index 100%
rename from src/plugin/email.ts
rename to src/plugin/communicate.ts
diff --git a/src/server.ts b/src/server.ts
index 7f86a63..8d8a73a 100644
--- a/src/server.ts
+++ b/src/server.ts
@@ -10,8 +10,8 @@ import Fastify, {
 import migrateDatabase from '@/migrator';
 import authPlugin from '@/plugin/auth';
 import cachePlugin from '@/plugin/cache';
+import emailPlugin from '@/plugin/communicate';
 import dbPlugin from '@/plugin/database';
-import emailPlugin from '@/plugin/email';
 import rateLimitPlugin from '@/plugin/rate-limit';
 import responsePlugin from '@/plugin/response';
 import sspPlugin from '@/plugin/ssp';
diff --git a/tests/plugin/email.test.ts b/tests/plugin/communicate.test.ts
similarity index 97%
rename from tests/plugin/email.test.ts
rename to tests/plugin/communicate.test.ts
index de75576..3b9ddb6 100644
--- a/tests/plugin/email.test.ts
+++ b/tests/plugin/communicate.test.ts
@@ -1,7 +1,7 @@
 import Fastify, {FastifyInstance} from 'fastify';
 import {afterEach, beforeEach, describe, expect, it, vi} from 'vitest';
 
-import emailPlugin from '@/plugin/email';
+import emailPlugin from '@/plugin/communicate';
 
 import {AppConfig} from '@/interfaces/config';
 
diff --git a/tests/server.test.ts b/tests/server.test.ts
index ee83493..dfb4b76 100644
--- a/tests/server.test.ts
+++ b/tests/server.test.ts
@@ -7,7 +7,7 @@ import Fastify, {
 import {afterEach, beforeEach, describe, expect, it, vi} from 'vitest';
 
 import migrateDatabase from '@/migrator/index';
-import emailPlugin from '@/plugin/email';
+import emailPlugin from '@/plugin/communicate';
 import {startServer} from '@/server';
 
 import {registerRoutes} from '@/routes/index';

From d5e2bf26acb55b733f8ac5a7a36b8ccb60411b18 Mon Sep 17 00:00:00 2001
From: Abhishek Chatterjee <abhishekchatterjeejit@gmail.com>
Date: Mon, 18 May 2026 18:24:02 +0530
Subject: [PATCH 3/3] feat(email): ROSS-168: nest email configuration under a
 new communicate module in config and codebase

---
 example_config.json              |  6 +++--
 src/interfaces/config.ts         |  6 ++++-
 src/plugin/communicate.ts        |  2 +-
 src/server.ts                    |  8 +++---
 src/validators/config/schema.ts  | 10 +++++++-
 tests/plugin/communicate.test.ts | 28 ++++++++++++--------
 tests/server.test.ts             | 28 ++++++++++----------
 tests/validators/config.test.ts  | 44 ++++++++++++++++++++++++--------
 8 files changed, 89 insertions(+), 43 deletions(-)

diff --git a/example_config.json b/example_config.json
index b5de3ef..eb2358f 100644
--- a/example_config.json
+++ b/example_config.json
@@ -52,8 +52,10 @@
             "passwordColumn": "password"
         }
     },
-    "email": {
-        "emailEngine": "dummy"
+    "communicate": {
+        "email": {
+            "emailEngine": "dummy"
+        }
     },
     "models": [
         {
diff --git a/src/interfaces/config.ts b/src/interfaces/config.ts
index f4b9942..e685fa3 100644
--- a/src/interfaces/config.ts
+++ b/src/interfaces/config.ts
@@ -216,6 +216,10 @@ export interface EmailConfig {
   emailEngine: EmailEngine;
 }
 
+export interface CommunicateConfig {
+  email?: EmailConfig;
+}
+
 export interface AppConfig {
   application: ApplicationConfig;
   swagger: SwaggerConfig;
@@ -225,5 +229,5 @@ export interface AppConfig {
   cache_db?: CacheDbConfig;
   customAPIs?: CustomAPIConfig;
   auth?: AuthConfig;
-  email?: EmailConfig;
+  communicate?: CommunicateConfig;
 }
diff --git a/src/plugin/communicate.ts b/src/plugin/communicate.ts
index 94be8df..853f440 100644
--- a/src/plugin/communicate.ts
+++ b/src/plugin/communicate.ts
@@ -14,7 +14,7 @@ const sendDummyEmail = async (
 export default fp(async (fastify: FastifyInstance) => {
   const communicate = {
     sendEmail: async (email: string, htmlBody: string, body: string) => {
-      if (fastify.appConfig.email.emailEngine === 'dummy') {
+      if (fastify.appConfig.communicate?.email?.emailEngine === 'dummy') {
         await sendDummyEmail(email, htmlBody, body);
       }
     },
diff --git a/src/server.ts b/src/server.ts
index 8d8a73a..f2bd6e9 100644
--- a/src/server.ts
+++ b/src/server.ts
@@ -10,7 +10,7 @@ import Fastify, {
 import migrateDatabase from '@/migrator';
 import authPlugin from '@/plugin/auth';
 import cachePlugin from '@/plugin/cache';
-import emailPlugin from '@/plugin/communicate';
+import communicatePlugin from '@/plugin/communicate';
 import dbPlugin from '@/plugin/database';
 import rateLimitPlugin from '@/plugin/rate-limit';
 import responsePlugin from '@/plugin/response';
@@ -122,9 +122,9 @@ export async function startServer(
   // config-driven cache (Redis or NodeCache)
   await app.register(cachePlugin);
 
-  // config-driven email
-  if (config.email) {
-    await app.register(emailPlugin);
+  // config-driven communicate
+  if (config.communicate) {
+    await app.register(communicatePlugin);
   }
 
   // config-driven rate limit
diff --git a/src/validators/config/schema.ts b/src/validators/config/schema.ts
index d282f75..f6a6d8d 100644
--- a/src/validators/config/schema.ts
+++ b/src/validators/config/schema.ts
@@ -474,6 +474,14 @@ const emailSchema = {
   },
 };
 
+const communicateSchema = {
+  type: 'object',
+  additionalProperties: false,
+  properties: {
+    email: emailSchema,
+  },
+};
+
 const schema = {
   type: 'object',
   required: ['application', 'swagger', 'database', 'models'],
@@ -491,7 +499,7 @@ const schema = {
     cache_db: cacheDbSchema,
     customAPIs: customAPIsSchema,
     auth: authSchema,
-    email: emailSchema,
+    communicate: communicateSchema,
   },
 };
 
diff --git a/tests/plugin/communicate.test.ts b/tests/plugin/communicate.test.ts
index 3b9ddb6..0b7f089 100644
--- a/tests/plugin/communicate.test.ts
+++ b/tests/plugin/communicate.test.ts
@@ -1,11 +1,11 @@
 import Fastify, {FastifyInstance} from 'fastify';
 import {afterEach, beforeEach, describe, expect, it, vi} from 'vitest';
 
-import emailPlugin from '@/plugin/communicate';
+import communicatePlugin from '@/plugin/communicate';
 
 import {AppConfig} from '@/interfaces/config';
 
-describe('email plugin', () => {
+describe('communicate plugin', () => {
   let app: FastifyInstance;
 
   beforeEach(() => {
@@ -21,12 +21,14 @@ describe('email plugin', () => {
   it('decorates fastify with communicate', async () => {
     app = Fastify();
     app.appConfig = {
-      email: {
-        emailEngine: 'dummy',
+      communicate: {
+        email: {
+          emailEngine: 'dummy',
+        },
       },
     } as unknown as AppConfig;
 
-    await app.register(emailPlugin);
+    await app.register(communicatePlugin);
     await app.ready();
 
     expect(app.hasDecorator('communicate')).toBe(true);
@@ -37,12 +39,14 @@ describe('email plugin', () => {
   it('sends a dummy email when emailEngine is dummy', async () => {
     app = Fastify();
     app.appConfig = {
-      email: {
-        emailEngine: 'dummy',
+      communicate: {
+        email: {
+          emailEngine: 'dummy',
+        },
       },
     } as unknown as AppConfig;
 
-    await app.register(emailPlugin);
+    await app.register(communicatePlugin);
     await app.ready();
 
     const consoleLogSpy = vi.spyOn(console, 'log').mockImplementation(() => {});
@@ -63,12 +67,14 @@ describe('email plugin', () => {
   it('does not send an email if emailEngine is not dummy', async () => {
     app = Fastify();
     app.appConfig = {
-      email: {
-        emailEngine: 'other' as unknown as 'dummy',
+      communicate: {
+        email: {
+          emailEngine: 'other' as unknown as 'dummy',
+        },
       },
     } as unknown as AppConfig;
 
-    await app.register(emailPlugin);
+    await app.register(communicatePlugin);
     await app.ready();
 
     const consoleLogSpy = vi.spyOn(console, 'log').mockImplementation(() => {});
diff --git a/tests/server.test.ts b/tests/server.test.ts
index dfb4b76..b261ccc 100644
--- a/tests/server.test.ts
+++ b/tests/server.test.ts
@@ -7,7 +7,7 @@ import Fastify, {
 import {afterEach, beforeEach, describe, expect, it, vi} from 'vitest';
 
 import migrateDatabase from '@/migrator/index';
-import emailPlugin from '@/plugin/communicate';
+import communicatePlugin from '@/plugin/communicate';
 import {startServer} from '@/server';
 
 import {registerRoutes} from '@/routes/index';
@@ -544,30 +544,32 @@ describe('Server', () => {
     });
   });
 
-  describe('Email Configuration', () => {
-    it('should register email plugin when email is configured', async () => {
-      const configWithEmail: AppConfig = {
+  describe('Communicate Configuration', () => {
+    it('should register communicate plugin when communicate is configured', async () => {
+      const configWithCommunicate: AppConfig = {
         ...mockConfig,
-        email: {
-          emailEngine: 'dummy',
+        communicate: {
+          email: {
+            emailEngine: 'dummy',
+          },
         },
       };
 
       const registerMock = mockApp.register;
-      await startServer(configWithEmail, 3000, 'dev');
+      await startServer(configWithCommunicate, 3000, 'dev');
 
-      expect(registerMock).toHaveBeenCalledWith(emailPlugin);
+      expect(registerMock).toHaveBeenCalledWith(communicatePlugin);
     });
 
-    it('should not register email plugin when email is not configured', async () => {
+    it('should not register communicate plugin when communicate is not configured', async () => {
       const registerMock = mockApp.register;
       await startServer(mockConfig, 3000, 'dev');
 
-      // Assert that none of the registered calls are the emailPlugin
-      const emailPluginCall = registerMock.mock.calls.find(
-        (call: unknown[]) => call[0] === emailPlugin,
+      // Assert that none of the registered calls are the communicatePlugin
+      const communicatePluginCall = registerMock.mock.calls.find(
+        (call: unknown[]) => call[0] === communicatePlugin,
       );
-      expect(emailPluginCall).toBeUndefined();
+      expect(communicatePluginCall).toBeUndefined();
     });
   });
 });
diff --git a/tests/validators/config.test.ts b/tests/validators/config.test.ts
index 5b54696..c9230ac 100644
--- a/tests/validators/config.test.ts
+++ b/tests/validators/config.test.ts
@@ -3467,13 +3467,15 @@ describe('validateValidAuthorizationConfig', () => {
   });
 });
 
-// check email configs validation
-describe('validateEmailConfig', () => {
-  it('should pass when email config is valid', () => {
+// check communicate configs validation
+describe('validateCommunicateConfig', () => {
+  it('should pass when communicate config is valid', () => {
     const config = {
       ...validBaseConfig,
-      email: {
-        emailEngine: 'dummy',
+      communicate: {
+        email: {
+          emailEngine: 'dummy',
+        },
       },
     };
 
@@ -3483,7 +3485,9 @@ describe('validateEmailConfig', () => {
   it('should throw when email config is missing required emailEngine', () => {
     const config = {
       ...validBaseConfig,
-      email: {},
+      communicate: {
+        email: {},
+      },
     };
 
     expect(() => validateConfig(config as unknown as AppConfig)).toThrow(
@@ -3494,8 +3498,10 @@ describe('validateEmailConfig', () => {
   it('should throw when email config has invalid emailEngine enum value', () => {
     const config = {
       ...validBaseConfig,
-      email: {
-        emailEngine: 'invalid-engine',
+      communicate: {
+        email: {
+          emailEngine: 'invalid-engine',
+        },
       },
     };
 
@@ -3507,8 +3513,26 @@ describe('validateEmailConfig', () => {
   it('should throw when email config has extra properties', () => {
     const config = {
       ...validBaseConfig,
-      email: {
-        emailEngine: 'dummy',
+      communicate: {
+        email: {
+          emailEngine: 'dummy',
+          extraProperty: true,
+        },
+      },
+    };
+
+    expect(() => validateConfig(config as unknown as AppConfig)).toThrow(
+      'must NOT have additional properties',
+    );
+  });
+
+  it('should throw when communicate config itself has extra properties', () => {
+    const config = {
+      ...validBaseConfig,
+      communicate: {
+        email: {
+          emailEngine: 'dummy',
+        },
         extraProperty: true,
       },
     };