test(@nestjs/config) add more tests for priority

These answer following questions.
both .env file and load configuration, what's the priority?
both multiple load configurations, what's the priority?

tests/e2e/load-priority.spec.ts

@@ -66,6 +66,47 @@ describe('Environment variables and .env files', () => {
     });
   });
 
+  describe('with conflicts of .env file and loaded configuration', () => {
+    beforeAll(async () => {
+      const moduleRef = await Test.createTestingModule({
+        imports: [
+          AppModule.withEnvVarsAndLoadedConfigurations([
+            () => ({ PORT: '8000' }),
+          ]),
+        ],
+      }).compile();
+
+      app = moduleRef.createNestApplication();
+      await app.init();
+    });
+
+    it('should choose .env file vars over load configuration', () => {
+      const configService = app.get(ConfigService);
+      expect(configService.get('PORT')).toEqual('4000');
+    });
+  });
+
+  describe('with conflicts of multiple loaded configurations', () => {
+    beforeAll(async () => {
+      const moduleRef = await Test.createTestingModule({
+        imports: [
+          AppModule.withDynamicLoadedConfigurations([
+            () => ({ PORT: '8000' }),
+            () => ({ PORT: '9000' }),
+          ]),
+        ],
+      }).compile();
+
+      app = moduleRef.createNestApplication();
+      await app.init();
+    });
+
+    it('should choose last load configuration', () => {
+      const configService = app.get(ConfigService);
+      expect(configService.get('PORT')).toEqual('9000');
+    });
+  });
+
   afterEach(async () => {
     process.env = {
       ...envBackup,

tests/src/app.module.ts

@@ -1,7 +1,7 @@
 import { DynamicModule, Inject, Module, Optional } from '@nestjs/common';
 import Joi from 'joi';
 import { join } from 'path';
-import { ConfigType } from '../../lib';
+import { ConfigFactory, ConfigType } from '../../lib';
 import { ConfigModule } from '../../lib/config.module';
 import { ConfigService } from '../../lib/config.service';
 import databaseConfig from './database.config';
@@ -98,7 +98,21 @@ export class AppModule {
       imports: [
         ConfigModule.forRoot({
           envFilePath: join(__dirname, '.env.expanded'),
-          expandVariables: { ignoreProcessEnv: true }
+          expandVariables: { ignoreProcessEnv: true },
+        }),
+      ],
+    };
+  }
+
+  static withEnvVarsAndLoadedConfigurations(
+    configFactory: ConfigFactory[],
+  ): DynamicModule {
+    return {
+      module: AppModule,
+      imports: [
+        ConfigModule.forRoot({
+          envFilePath: join(__dirname, '.env'),
+          load: configFactory,
         }),
       ],
     };
@@ -137,6 +151,19 @@ export class AppModule {
     };
   }
 
+  static withDynamicLoadedConfigurations(
+    configFactory: ConfigFactory[],
+  ): DynamicModule {
+    return {
+      module: AppModule,
+      imports: [
+        ConfigModule.forRoot({
+          load: configFactory,
+        }),
+      ],
+    };
+  }
+
   static withSchemaValidation(
     envFilePath?: string,
     ignoreEnvFile?: boolean,