refactor(core): add optional decorator

packages/container/libraries/core/src/metadata/decorators/optional.int.spec.ts

@@ -0,0 +1,84 @@
+import { beforeAll, describe, expect, it } from '@jest/globals';
+
+import 'reflect-metadata';
+
+import { getReflectMetadata } from '@inversifyjs/reflect-metadata-utils';
+
+import { classMetadataReflectKey } from '../../reflectMetadata/data/classMetadataReflectKey';
+import { MaybeClassElementMetadataKind } from '../models/MaybeClassElementMetadataKind';
+import { MaybeClassMetadata } from '../models/MaybeClassMetadata';
+import { optional } from './optional';
+
+describe(optional.name, () => {
+  describe('when called', () => {
+    let result: unknown;
+
+    beforeAll(() => {
+      class Foo {
+        @optional()
+        public readonly bar!: string;
+
+        @optional()
+        public readonly baz!: string;
+
+        constructor(
+          @optional()
+          public firstParam: number,
+          @optional()
+          public secondParam: number,
+        ) {}
+      }
+
+      result = getReflectMetadata(Foo, classMetadataReflectKey);
+    });
+
+    it('should return expected metadata', () => {
+      const expected: MaybeClassMetadata = {
+        constructorArguments: [
+          {
+            kind: MaybeClassElementMetadataKind.unknown,
+            name: undefined,
+            optional: true,
+            tags: new Map(),
+            targetName: undefined,
+          },
+          {
+            kind: MaybeClassElementMetadataKind.unknown,
+            name: undefined,
+            optional: true,
+            tags: new Map(),
+            targetName: undefined,
+          },
+        ],
+        lifecycle: {
+          postConstructMethodName: undefined,
+          preDestroyMethodName: undefined,
+        },
+        properties: new Map([
+          [
+            'bar',
+            {
+              kind: MaybeClassElementMetadataKind.unknown,
+              name: undefined,
+              optional: true,
+              tags: new Map(),
+              targetName: undefined,
+            },
+          ],
+          [
+            'baz',
+            {
+              kind: MaybeClassElementMetadataKind.unknown,
+              name: undefined,
+              optional: true,
+              tags: new Map(),
+              targetName: undefined,
+            },
+          ],
+        ]),
+      };
+
+      expect(result).toStrictEqual(expected);
+    });
+  });
+});