创建一个管道pipe，demo

src/core/pipes/demo.pipe.spec.ts

@@ -0,0 +1,7 @@
+import { DemoPipe } from './demo.pipe';
+
+describe('DemoPipe', () => {
+  it('should be defined', () => {
+    expect(new DemoPipe()).toBeDefined();
+  });
+});

src/core/pipes/demo.pipe.ts

@@ -0,0 +1,8 @@
+import { ArgumentMetadata, Injectable, PipeTransform } from '@nestjs/common';
+
+@Injectable()
+export class DemoPipe implements PipeTransform {
+  transform(value: any, metadata: ArgumentMetadata) {
+    return value;
+  }
+}