feat: Add ConstantMetadataWriter.

test/unit/ldp/http/metadata/ConstantMetadataWriter.test.ts

@@ -0,0 +1,23 @@
+import { createResponse } from 'node-mocks-http';
+import { ConstantMetadataWriter } from '../../../../../src/ldp/http/metadata/ConstantMetadataWriter';
+
+describe('A ConstantMetadataWriter', (): void => {
+  const writer = new ConstantMetadataWriter({ 'custom-Header': 'X', other: 'Y' });
+
+  it('adds new headers.', async(): Promise<void> => {
+    const response = createResponse();
+
+    await expect(writer.handle({ response })).resolves.toBeUndefined();
+
+    expect(response.getHeaders()).toEqual({ 'custom-header': 'X', other: 'Y' });
+  });
+
+  it('extends existing headers.', async(): Promise<void> => {
+    const response = createResponse();
+    response.setHeader('Other', 'A');
+
+    await expect(writer.handle({ response })).resolves.toBeUndefined();
+
+    expect(response.getHeaders()).toEqual({ 'custom-header': 'X', other: [ 'A', 'Y' ]});
+  });
+});