Add unit tests.

src/core/server/logging/appenders/rewrite/mocks.ts

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+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+import type { RewritePolicy } from './policies/policy';
+
+const createPolicyMock = () => {
+  const mock: jest.Mocked<RewritePolicy> = {
+    transform: jest.fn((x) => x),
+  };
+  return mock;
+};
+
+export const rewriteAppenderMocks = {
+  createPolicy: createPolicyMock,
+};

src/core/server/logging/appenders/rewrite/policies/meta/meta_policy.test.ts

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+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+import { LogRecord, LogLevel, LogMeta } from '@kbn/logging';
+import { MetaRewritePolicy, MetaRewritePolicyConfig } from './meta_policy';
+
+describe('MetaRewritePolicy', () => {
+  const createPolicy = (
+    mode: MetaRewritePolicyConfig['mode'],
+    properties: MetaRewritePolicyConfig['properties']
+  ) => new MetaRewritePolicy({ type: 'meta', mode, properties });
+
+  const createLogRecord = (meta: LogMeta = {}): LogRecord => ({
+    timestamp: new Date(),
+    level: LogLevel.Info,
+    context: 'context',
+    message: 'just a log',
+    pid: 42,
+    meta,
+  });
+
+  describe('mode: add', () => {
+    it('adds new properties to LogMeta', () => {
+      const policy = createPolicy('add', [{ path: 'foo', value: 'bar' }]);
+      const log = createLogRecord();
+      expect(policy.transform(log).meta).toMatchInlineSnapshot(`
+        Object {
+          "foo": "bar",
+        }
+      `);
+    });
+
+    it('adds nested properties to LogMeta', () => {
+      const policy = createPolicy('add', [
+        { path: 'a.b', value: 'foo' },
+        { path: 'a.c[1]', value: 'bar' },
+      ]);
+      const log = createLogRecord();
+      expect(policy.transform(log).meta).toMatchInlineSnapshot(`
+        Object {
+          "a": Object {
+            "b": "foo",
+            "c": Array [
+              undefined,
+              "bar",
+            ],
+          },
+        }
+      `);
+    });
+
+    it('handles string, number, boolean, null', () => {
+      const policy = createPolicy('add', [
+        { path: 'boolean', value: false },
+        { path: 'null', value: null },
+        { path: 'number', value: 123 },
+        { path: 'string', value: 'hi' },
+      ]);
+      const log = createLogRecord();
+      expect(policy.transform(log).meta).toMatchInlineSnapshot(`
+        Object {
+          "boolean": false,
+          "null": null,
+          "number": 123,
+          "string": "hi",
+        }
+      `);
+    });
+
+    it('does not overwrite properties which already exist', () => {
+      const policy = createPolicy('add', [
+        { path: 'a.b', value: 'foo' },
+        { path: 'a.c', value: 'bar' },
+      ]);
+      const log = createLogRecord({ a: { b: 'existing meta' } });
+      const { meta } = policy.transform(log);
+      expect(meta!.a.b).toBe('existing meta');
+      expect(meta!.a.c).toBe('bar');
+    });
+
+    it('does not touch anything outside of LogMeta', () => {
+      const policy = createPolicy('add', [{ path: 'foo', value: 'bar' }]);
+      const message = Symbol();
+      expect(policy.transform(({ message } as unknown) as LogRecord).message).toBe(message);
+      expect(policy.transform(({ message } as unknown) as LogRecord)).toMatchInlineSnapshot(`
+        Object {
+          "message": Symbol(),
+          "meta": Object {
+            "foo": "bar",
+          },
+        }
+      `);
+    });
+  });
+
+  describe('mode: update', () => {
+    it('updates existing properties in LogMeta', () => {
+      const log = createLogRecord({ a: 'before' });
+      const policy = createPolicy('update', [{ path: 'a', value: 'after' }]);
+      expect(policy.transform(log).meta!.a).toBe('after');
+    });
+
+    it('updates nested properties in LogMeta', () => {
+      const log = createLogRecord({ a: 'before a', b: { c: 'before b.c' }, d: [0, 1] });
+      const policy = createPolicy('update', [
+        { path: 'a', value: 'after a' },
+        { path: 'b.c', value: 'after b.c' },
+        { path: 'd[1]', value: 2 },
+      ]);
+      expect(policy.transform(log).meta).toMatchInlineSnapshot(`
+        Object {
+          "a": "after a",
+          "b": Object {
+            "c": "after b.c",
+          },
+          "d": Array [
+            0,
+            2,
+          ],
+        }
+      `);
+    });
+
+    it('handles string, number, boolean, null', () => {
+      const policy = createPolicy('update', [
+        { path: 'a', value: false },
+        { path: 'b', value: null },
+        { path: 'c', value: 123 },
+        { path: 'd', value: 'hi' },
+      ]);
+      const log = createLogRecord({
+        a: 'a',
+        b: 'b',
+        c: 'c',
+        d: 'd',
+      });
+      expect(policy.transform(log).meta).toMatchInlineSnapshot(`
+        Object {
+          "a": false,
+          "b": null,
+          "c": 123,
+          "d": "hi",
+        }
+      `);
+    });
+
+    it(`does not add properties which don't exist yet`, () => {
+      const policy = createPolicy('update', [
+        { path: 'a.b', value: 'foo' },
+        { path: 'a.c', value: 'bar' },
+      ]);
+      const log = createLogRecord({ a: { b: 'existing meta' } });
+      const { meta } = policy.transform(log);
+      expect(meta!.a.b).toBe('foo');
+      expect(meta!.a.c).toBeUndefined();
+    });
+
+    it('does not touch anything outside of LogMeta', () => {
+      const policy = createPolicy('update', [{ path: 'a', value: 'bar' }]);
+      const message = Symbol();
+      expect(
+        policy.transform(({ message, meta: { a: 'foo' } } as unknown) as LogRecord).message
+      ).toBe(message);
+      expect(policy.transform(({ message, meta: { a: 'foo' } } as unknown) as LogRecord))
+        .toMatchInlineSnapshot(`
+        Object {
+          "message": Symbol(),
+          "meta": Object {
+            "a": "bar",
+          },
+        }
+      `);
+    });
+  });
+
+  describe('mode: remove', () => {
+    it('removes existing properties in LogMeta', () => {
+      const log = createLogRecord({ a: 'goodbye' });
+      const policy = createPolicy('remove', [{ path: 'a' }]);
+      expect(policy.transform(log).meta!.a).toBeUndefined();
+    });
+
+    it('removes nested properties in LogMeta', () => {
+      const log = createLogRecord({ a: 'a', b: { c: 'b.c' }, d: [0, 1] });
+      const policy = createPolicy('remove', [{ path: 'b.c' }, { path: 'd[1]' }]);
+      expect(policy.transform(log).meta).toMatchInlineSnapshot(`
+        Object {
+          "a": "a",
+          "b": Object {},
+          "d": Array [
+            0,
+            undefined,
+          ],
+        }
+      `);
+    });
+
+    it('has no effect if property does not exist', () => {
+      const log = createLogRecord({ a: 'a' });
+      const policy = createPolicy('remove', [{ path: 'b' }]);
+      expect(policy.transform(log).meta).toMatchInlineSnapshot(`
+        Object {
+          "a": "a",
+        }
+      `);
+    });
+
+    it('does not touch anything outside of LogMeta', () => {
+      const policy = createPolicy('remove', [{ path: 'a' }]);
+      const message = Symbol();
+      expect(
+        policy.transform(({ message, meta: { a: 'foo' } } as unknown) as LogRecord).message
+      ).toBe(message);
+      expect(policy.transform(({ message, meta: { a: 'foo' } } as unknown) as LogRecord))
+        .toMatchInlineSnapshot(`
+        Object {
+          "message": Symbol(),
+          "meta": Object {},
+        }
+      `);
+    });
+  });
+});

src/core/server/logging/appenders/rewrite/rewrite_appender.test.mocks.ts

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+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+import { schema } from '@kbn/config-schema';
+
+export const createRewritePolicyMock = jest.fn();
+jest.doMock('./policies', () => ({
+  rewritePolicyConfigSchema: schema.any(),
+  createRewritePolicy: createRewritePolicyMock,
+}));
+
+export const resetAllMocks = () => {
+  createRewritePolicyMock.mockReset();
+};