Better story around modules structure

src/app-module.ts

@@ -2,11 +2,9 @@ import { Module } from "@nestjs/common";
 
 import { AppController } from "./app-controller";
 import { AppService } from "./app-service";
-import { ConfigModule } from "./config";
 
 @Module({
-    imports: [ConfigModule],
     providers: [AppService],
     controllers: [AppController],
 })
-export class AppModule {}
+export class AppModule { }

src/config.ts

@@ -1,4 +1,4 @@
-import { Module } from "@nestjs/common";
+import { Module, Global } from "@nestjs/common";
 import * as dotenv from "dotenv";
 import * as fs from "fs";
 
@@ -11,9 +11,18 @@ export class ConfigService {
         return new ConfigService(envConfig);
     }
 
-    private readonly envConfig: {[prop: string]: string};
+    /**
+     * In tests, an _empty_ config will be generated. Tests will have to
+     * fake the calls to various config values, just like they'd do for
+     * other dependencies.
+     */
+    public static forTesting(): ConfigService {
+        return new ConfigService({});
+    }
+
+    private readonly envConfig: { [prop: string]: string };
 
-    constructor(envConfig?: {[prop: string]: string}) {
+    constructor(envConfig?: { [prop: string]: string }) {
         this.envConfig = envConfig || {};
     }
 
@@ -28,11 +37,22 @@ export class ConfigService {
     }
 }
 
+@Global()
 @Module({
     providers: [{
         provide: ConfigService,
         useValue: ConfigService.fromFile(".env"),
     }],
     exports: [ConfigService],
 })
-export class ConfigModule {}
+export class ConfigModule { }
+
+@Global()
+@Module({
+    providers: [{
+        provide: ConfigService,
+        useValue: ConfigService.forTesting(),
+    }],
+    exports: [ConfigService],
+})
+export class ConfigTestingModule { }

test/app-controller-test.ts

@@ -6,13 +6,14 @@ import * as sinon from "sinon";
 import { AppController } from "../src/app-controller";
 import { AppModule } from "../src/app-module";
 import { AppService } from "../src/app-service";
+import { ConfigTestingModule } from "../src/config";
 
 describe("AppController", () => {
     let module: TestingModule;
 
     beforeEach(async () => {
         module = await Test.createTestingModule({
-            imports: [AppModule],
+            imports: [AppModule, ConfigTestingModule],
         }).compile();
     });
 

test/app-service-test.ts

@@ -6,14 +6,14 @@ import * as sinon from "sinon";
 import { AppModule } from "../src/app-module";
 import { AppService } from "../src/app-service";
 import { Env } from "../src/common";
-import { ConfigService } from "../src/config";
+import { ConfigService, ConfigTestingModule } from "../src/config";
 
 describe("AppService", () => {
     let module: TestingModule;
 
     beforeEach(async () => {
         module = await Test.createTestingModule({
-            imports: [AppModule],
+            imports: [AppModule, ConfigTestingModule],
         }).compile();
     });
 

test/config-test.ts

@@ -28,4 +28,11 @@ PORT=10001
         expect(configService.env).to.eql(Env.Test);
         expect(configService.port).to.eql(10001);
     });
+
+    it("can be constructed for testing", () => {
+        const configService = ConfigService.forTesting();
+
+        expect(() => configService.env).to.throw;
+        expect(() => configService.port).to.throw;
+    });
 });