diff --git a/README.md b/README.md
index a2f98b8..6e56fc8 100644
--- a/README.md
+++ b/README.md
@@ -63,6 +63,7 @@ This goal of this project is to help you get better at Angular and NgRx by resol
 <a href="./apps/testing-nested/README.md"><img src="https://img.shields.io/badge/18-Nested Comp Testing-orange" alt="nested component Testing"/></a>
 <a href="./apps/testing-input-output/README.md"><img src="https://img.shields.io/badge/19-Input Output Testing-orange" alt="input output Testing"/></a>
 <a href="./apps/testing-modal/README.md"><img src="https://img.shields.io/badge/20-Modal Testing-orange" alt="modal Testing"/></a>
+<a href="./apps/testing-harness/README.md"><img src="https://img.shields.io/badge/23-Harness Testing-green" alt="harness Testing"/></a>
 
 ## Contributors ✨
 
@@ -72,7 +73,7 @@ This goal of this project is to help you get better at Angular and NgRx by resol
 <table>
   <tbody>
     <tr>
-      <td align="center" valign="top" width="14.28%"><a href="https://medium.com/@thomas.laforge"><img src="https://avatars.githubusercontent.com/u/30832608?s…00&u=6f0ad9676792f29fd7fe6e113df06213d384a813&v=4" width="100px;" alt="Thomas Laforge"/><br /><sub><b>Thomas Laforge</b></sub></a><br />21 🧩</a></td>
+      <td align="center" valign="top" width="14.28%"><a href="https://medium.com/@thomas.laforge"><img src="https://avatars.githubusercontent.com/u/30832608?s…00&u=6f0ad9676792f29fd7fe6e113df06213d384a813&v=4" width="100px;" alt="Thomas Laforge"/><br /><sub><b>Thomas Laforge</b></sub></a><br />23 🧩</a></td>
     </tr>
   </tbody>
 </table>
diff --git a/apps/testing-harness/.eslintrc.json b/apps/testing-harness/.eslintrc.json
new file mode 100644
index 0000000..b428c22
--- /dev/null
+++ b/apps/testing-harness/.eslintrc.json
@@ -0,0 +1,36 @@
+{
+  "extends": ["../../.eslintrc.json"],
+  "ignorePatterns": ["!**/*"],
+  "overrides": [
+    {
+      "files": ["*.ts"],
+      "rules": {
+        "@angular-eslint/directive-selector": [
+          "error",
+          {
+            "type": "attribute",
+            "prefix": "app",
+            "style": "camelCase"
+          }
+        ],
+        "@angular-eslint/component-selector": [
+          "error",
+          {
+            "type": "element",
+            "prefix": "app",
+            "style": "kebab-case"
+          }
+        ]
+      },
+      "extends": [
+        "plugin:@nx/angular",
+        "plugin:@angular-eslint/template/process-inline-templates"
+      ]
+    },
+    {
+      "files": ["*.html"],
+      "extends": ["plugin:@nx/angular-template"],
+      "rules": {}
+    }
+  ]
+}
diff --git a/apps/testing-harness/README.md b/apps/testing-harness/README.md
new file mode 100644
index 0000000..75182b8
--- /dev/null
+++ b/apps/testing-harness/README.md
@@ -0,0 +1,32 @@
+<h1>Testing with Angular CDK Harness</h1>
+
+> Author: Thomas Laforge
+
+### Statement:
+
+The objective of this challenge is to have a better understanding of the CDK test harness API. In this initial challenge, we will only use Angular Material's built-in harnesses.
+
+The goal is to test the functionality of `child.component.ts`. I have prepared a test suite that you need to implement, but feel free to include additional tests as well.
+
+**Note:** You are welcome to use Testing Library if you wish.
+
+Documentation for CDK Component Harness is [here](https://material.angular.io/cdk/test-harnesses/overview#api-for-test-authors)
+Documentation for Angular Material component is [here](https://material.angular.io/components/button/overview)
+
+### Submitting your work
+
+1. Fork the project
+2. clone it
+3. npm install
+4. `npx nx serve testing-harness` to play with the application
+5. `npx nx test testing-harness` to test your application with Testing Library
+6. _...work on it_
+7. Commit your work
+8. Submit a PR with a title beginning with **Answer:23** that I will review and other dev can review.
+
+<a href="https://github.com/tomalaforge/angular-challenges/pulls?q=label%3A23+label%3Aanswer"><img src="https://img.shields.io/badge/-Solutions-green" alt="harness testing"/></a>
+<a href='https://github.com/tomalaforge/angular-challenges/pulls?q=label%3A23+label%3A"answer+author"'><img src="https://img.shields.io/badge/-Author solution-important" alt="harness testing solution author"/></a>
+
+<!-- <a href="{Blog post url}" target="_blank" rel="noopener noreferrer"><img src="https://img.shields.io/badge/-Blog post explanation-blue" alt="nested testing blog article"/></a> -->
+
+_You can ask any question on_ <a href="https://twitter.com/laforge_toma" target="_blank" rel="noopener noreferrer"><img src="./../../logo/twitter.svg" height=20px alt="twitter"/></a>
diff --git a/apps/testing-harness/jest.config.ts b/apps/testing-harness/jest.config.ts
new file mode 100644
index 0000000..1a72238
--- /dev/null
+++ b/apps/testing-harness/jest.config.ts
@@ -0,0 +1,21 @@
+/* eslint-disable */
+export default {
+  displayName: 'testing-harness',
+  preset: '../../jest.preset.js',
+  setupFilesAfterEnv: ['<rootDir>/src/test-setup.ts'],
+  transform: {
+    '^.+\\.(ts|mjs|js|html)$': [
+      'jest-preset-angular',
+      {
+        tsconfig: '<rootDir>/tsconfig.spec.json',
+        stringifyContentPathRegex: '\\.(html|svg)$',
+      },
+    ],
+  },
+  transformIgnorePatterns: ['node_modules/(?!.*\\.mjs$)'],
+  snapshotSerializers: [
+    'jest-preset-angular/build/serializers/no-ng-attributes',
+    'jest-preset-angular/build/serializers/ng-snapshot',
+    'jest-preset-angular/build/serializers/html-comment',
+  ],
+};
diff --git a/apps/testing-harness/project.json b/apps/testing-harness/project.json
new file mode 100644
index 0000000..3b93c76
--- /dev/null
+++ b/apps/testing-harness/project.json
@@ -0,0 +1,95 @@
+{
+  "name": "testing-harness",
+  "$schema": "../../node_modules/nx/schemas/project-schema.json",
+  "projectType": "application",
+  "prefix": "app",
+  "sourceRoot": "apps/testing-harness/src",
+  "tags": [],
+  "targets": {
+    "build": {
+      "executor": "@angular-devkit/build-angular:browser",
+      "outputs": ["{options.outputPath}"],
+      "options": {
+        "outputPath": "dist/apps/testing-harness",
+        "index": "apps/testing-harness/src/index.html",
+        "main": "apps/testing-harness/src/main.ts",
+        "polyfills": ["zone.js"],
+        "tsConfig": "apps/testing-harness/tsconfig.app.json",
+        "assets": [
+          "apps/testing-harness/src/favicon.ico",
+          "apps/testing-harness/src/assets"
+        ],
+        "styles": ["apps/testing-harness/src/styles.scss"],
+        "scripts": []
+      },
+      "configurations": {
+        "production": {
+          "budgets": [
+            {
+              "type": "initial",
+              "maximumWarning": "500kb",
+              "maximumError": "1mb"
+            },
+            {
+              "type": "anyComponentStyle",
+              "maximumWarning": "2kb",
+              "maximumError": "4kb"
+            }
+          ],
+          "outputHashing": "all"
+        },
+        "development": {
+          "buildOptimizer": false,
+          "optimization": false,
+          "vendorChunk": true,
+          "extractLicenses": false,
+          "sourceMap": true,
+          "namedChunks": true
+        }
+      },
+      "defaultConfiguration": "production"
+    },
+    "serve": {
+      "executor": "@angular-devkit/build-angular:dev-server",
+      "configurations": {
+        "production": {
+          "browserTarget": "testing-harness:build:production"
+        },
+        "development": {
+          "browserTarget": "testing-harness:build:development"
+        }
+      },
+      "defaultConfiguration": "development"
+    },
+    "extract-i18n": {
+      "executor": "@angular-devkit/build-angular:extract-i18n",
+      "options": {
+        "browserTarget": "testing-harness:build"
+      }
+    },
+    "test": {
+      "executor": "@nx/jest:jest",
+      "outputs": ["{workspaceRoot}/coverage/{projectRoot}"],
+      "options": {
+        "jestConfig": "apps/testing-harness/jest.config.ts",
+        "passWithNoTests": true
+      },
+      "configurations": {
+        "ci": {
+          "ci": true,
+          "codeCoverage": true
+        }
+      }
+    },
+    "lint": {
+      "executor": "@nx/linter:eslint",
+      "outputs": ["{options.outputFile}"],
+      "options": {
+        "lintFilePatterns": [
+          "apps/testing-harness/**/*.ts",
+          "apps/testing-harness/**/*.html"
+        ]
+      }
+    }
+  }
+}
diff --git a/apps/testing-harness/src/app/app.component.ts b/apps/testing-harness/src/app/app.component.ts
new file mode 100644
index 0000000..76ccd4d
--- /dev/null
+++ b/apps/testing-harness/src/app/app.component.ts
@@ -0,0 +1,11 @@
+import { Component } from '@angular/core';
+import { ChildComponent } from './child.component';
+
+@Component({
+  standalone: true,
+  imports: [ChildComponent],
+  selector: 'app-root',
+  template: `<app-child />`,
+  styles: [''],
+})
+export class AppComponent {}
diff --git a/apps/testing-harness/src/app/app.config.ts b/apps/testing-harness/src/app/app.config.ts
new file mode 100644
index 0000000..59198e6
--- /dev/null
+++ b/apps/testing-harness/src/app/app.config.ts
@@ -0,0 +1,6 @@
+import { ApplicationConfig } from '@angular/core';
+import { provideAnimations } from '@angular/platform-browser/animations';
+
+export const appConfig: ApplicationConfig = {
+  providers: [provideAnimations()],
+};
diff --git a/apps/testing-harness/src/app/child.component.spec.ts b/apps/testing-harness/src/app/child.component.spec.ts
new file mode 100644
index 0000000..8e888b3
--- /dev/null
+++ b/apps/testing-harness/src/app/child.component.spec.ts
@@ -0,0 +1,28 @@
+import { render } from '@testing-library/angular';
+import { ChildComponent } from './child.component';
+
+describe('ChildComponent', () => {
+  test('should have 1 slider, 3 checkboxes, 4 inputs, 2 buttons', async () => {
+    await render(ChildComponent);
+  });
+
+  test('should get initial value of slider thumb', async () => {
+    await render(ChildComponent);
+  });
+
+  test('set maxValue to 109 and slider max value should be 109', async () => {
+    await render(ChildComponent);
+  });
+
+  test('toggle disabled checkbox and slider should be disabled', async () => {
+    await render(ChildComponent);
+  });
+
+  test('set step value to 5 and click to forward button two times, thumb value should be 10', async () => {
+    await render(ChildComponent);
+  });
+
+  test('slider value is 5, set step value to 6, click on back button, slider value should still be 5', async () => {
+    await render(ChildComponent);
+  });
+});
diff --git a/apps/testing-harness/src/app/child.component.ts b/apps/testing-harness/src/app/child.component.ts
new file mode 100644
index 0000000..178c06c
--- /dev/null
+++ b/apps/testing-harness/src/app/child.component.ts
@@ -0,0 +1,120 @@
+import { Component } from '@angular/core';
+import { FormsModule } from '@angular/forms';
+import { MatCardModule } from '@angular/material/card';
+import { MatCheckboxModule } from '@angular/material/checkbox';
+import { MatFormFieldModule } from '@angular/material/form-field';
+import { MatIconModule } from '@angular/material/icon';
+import { MatInputModule } from '@angular/material/input';
+import { MatSliderModule } from '@angular/material/slider';
+
+@Component({
+  selector: 'app-child',
+  template: `
+    <mat-card>
+      <mat-card-content>
+        <h2 class="my-3">Slider configuration</h2>
+
+        <section class="flex items-center">
+          <mat-form-field class="m-4 max-w-[180px] w-full">
+            <mat-label>Value</mat-label>
+            <input
+              matInput
+              type="number"
+              [(ngModel)]="value"
+              id="input-value" />
+          </mat-form-field>
+          <mat-form-field class="m-4 max-w-[180px] w-full">
+            <mat-label>Min value</mat-label>
+            <input matInput type="number" [(ngModel)]="min" id="input-min" />
+          </mat-form-field>
+          <mat-form-field class="m-4 max-w-[180px] w-full">
+            <mat-label>Max value</mat-label>
+            <input matInput type="number" [(ngModel)]="max" id="input-max" />
+          </mat-form-field>
+          <mat-form-field class="m-4 max-w-[180px] w-full">
+            <mat-label>Step size</mat-label>
+            <input matInput type="number" [(ngModel)]="step" id="input-step" />
+          </mat-form-field>
+        </section>
+
+        <section class="flex items-center">
+          <mat-checkbox [(ngModel)]="showTicks">Show ticks</mat-checkbox>
+        </section>
+
+        <section class="flex items-center">
+          <mat-checkbox [(ngModel)]="thumbLabel">Show thumb label</mat-checkbox>
+        </section>
+
+        <section class="flex items-center">
+          <mat-checkbox [(ngModel)]="disabled">Disabled</mat-checkbox>
+        </section>
+      </mat-card-content>
+    </mat-card>
+
+    <mat-card class="flex">
+      <mat-card-content>
+        <div class="flex gap-10">
+          <button mat-mini-fab (click)="back()">
+            <mat-icon>arrow_back_ios</mat-icon>
+          </button>
+          <mat-slider
+            class="m-4"
+            [disabled]="disabled"
+            [max]="max"
+            [min]="min"
+            [step]="step"
+            [discrete]="thumbLabel"
+            [showTickMarks]="showTicks">
+            <input matSliderThumb [(ngModel)]="value" />
+          </mat-slider>
+          <button mat-mini-fab (click)="forward()">
+            <mat-icon>arrow_forward_ios</mat-icon>
+          </button>
+        </div>
+      </mat-card-content>
+    </mat-card>
+  `,
+  styles: [
+    `
+      .mat-mdc-slider {
+        max-width: 300px;
+        width: 100%;
+      }
+
+      .mat-mdc-card + .mat-mdc-card {
+        margin-top: 8px;
+      }
+    `,
+  ],
+  standalone: true,
+  imports: [
+    MatCardModule,
+    MatFormFieldModule,
+    MatInputModule,
+    FormsModule,
+    MatCheckboxModule,
+    MatSliderModule,
+    MatIconModule,
+  ],
+})
+export class ChildComponent {
+  disabled = false;
+  max = 100;
+  min = 0;
+  showTicks = false;
+  step = 1;
+  thumbLabel = false;
+  value = 0;
+
+  back() {
+    if (this.value - this.step >= this.min) {
+      this.value -= this.step;
+    }
+  }
+
+  forward() {
+    if (this.value + this.step <= this.max) {
+      this.value += this.step;
+    }
+  }
+}
diff --git a/apps/testing-harness/src/assets/.gitkeep b/apps/testing-harness/src/assets/.gitkeep
new file mode 100644
index 0000000..e69de29
diff --git a/apps/testing-harness/src/favicon.ico b/apps/testing-harness/src/favicon.ico
new file mode 100644
index 0000000..317ebcb
Binary files /dev/null and b/apps/testing-harness/src/favicon.ico differ
diff --git a/apps/testing-harness/src/index.html b/apps/testing-harness/src/index.html
new file mode 100644
index 0000000..1141708
--- /dev/null
+++ b/apps/testing-harness/src/index.html
@@ -0,0 +1,16 @@
+<!DOCTYPE html>
+<html lang="en">
+  <head>
+    <meta charset="utf-8" />
+    <title>harness</title>
+    <base href="/" />
+    <meta name="viewport" content="width=device-width, initial-scale=1" />
+    <link rel="icon" type="image/x-icon" href="favicon.ico" />
+    <link
+      href="https://fonts.googleapis.com/icon?family=Material+Icons"
+      rel="stylesheet" />
+  </head>
+  <body>
+    <app-root></app-root>
+  </body>
+</html>
diff --git a/apps/testing-harness/src/main.ts b/apps/testing-harness/src/main.ts
new file mode 100644
index 0000000..514c89a
--- /dev/null
+++ b/apps/testing-harness/src/main.ts
@@ -0,0 +1,7 @@
+import { bootstrapApplication } from '@angular/platform-browser';
+import { appConfig } from './app/app.config';
+import { AppComponent } from './app/app.component';
+
+bootstrapApplication(AppComponent, appConfig).catch((err) =>
+  console.error(err)
+);
diff --git a/apps/testing-harness/src/styles.scss b/apps/testing-harness/src/styles.scss
new file mode 100644
index 0000000..c9c067e
--- /dev/null
+++ b/apps/testing-harness/src/styles.scss
@@ -0,0 +1,28 @@
+@use '@angular/material' as mat;
+
+@tailwind base;
+@tailwind components;
+@tailwind utilities;
+
+/* You can add global styles to this file, and also import other style files */
+
+@include mat.core();
+
+$theme-primary: mat.define-palette(mat.$indigo-palette);
+$theme-accent: mat.define-palette(mat.$pink-palette, A200, A100, A400);
+
+$theme-warn: mat.define-palette(mat.$red-palette);
+
+$theme: mat.define-light-theme(
+  (
+    color: (
+      primary: $theme-primary,
+      accent: $theme-accent,
+      warn: $theme-warn,
+    ),
+    typography: mat.define-typography-config(),
+  )
+);
+
+@include mat.dialog-theme($theme);
+@include mat.all-component-themes($theme);
diff --git a/apps/testing-harness/src/test-setup.ts b/apps/testing-harness/src/test-setup.ts
new file mode 100644
index 0000000..15de72a
--- /dev/null
+++ b/apps/testing-harness/src/test-setup.ts
@@ -0,0 +1,2 @@
+import '@testing-library/jest-dom';
+import 'jest-preset-angular/setup-jest';
diff --git a/apps/testing-harness/tailwind.config.js b/apps/testing-harness/tailwind.config.js
new file mode 100644
index 0000000..38183db
--- /dev/null
+++ b/apps/testing-harness/tailwind.config.js
@@ -0,0 +1,14 @@
+const { createGlobPatternsForDependencies } = require('@nx/angular/tailwind');
+const { join } = require('path');
+
+/** @type {import('tailwindcss').Config} */
+module.exports = {
+  content: [
+    join(__dirname, 'src/**/!(*.stories|*.spec).{ts,html}'),
+    ...createGlobPatternsForDependencies(__dirname),
+  ],
+  theme: {
+    extend: {},
+  },
+  plugins: [],
+};
diff --git a/apps/testing-harness/tsconfig.app.json b/apps/testing-harness/tsconfig.app.json
new file mode 100644
index 0000000..fff4a41
--- /dev/null
+++ b/apps/testing-harness/tsconfig.app.json
@@ -0,0 +1,10 @@
+{
+  "extends": "./tsconfig.json",
+  "compilerOptions": {
+    "outDir": "../../dist/out-tsc",
+    "types": []
+  },
+  "files": ["src/main.ts"],
+  "include": ["src/**/*.d.ts"],
+  "exclude": ["jest.config.ts", "src/**/*.test.ts", "src/**/*.spec.ts"]
+}
diff --git a/apps/testing-harness/tsconfig.editor.json b/apps/testing-harness/tsconfig.editor.json
new file mode 100644
index 0000000..6763401
--- /dev/null
+++ b/apps/testing-harness/tsconfig.editor.json
@@ -0,0 +1,7 @@
+{
+  "extends": "./tsconfig.json",
+  "include": ["src/**/*.ts", "jest.config.ts"],
+  "compilerOptions": {
+    "types": []
+  }
+}
diff --git a/apps/testing-harness/tsconfig.json b/apps/testing-harness/tsconfig.json
new file mode 100644
index 0000000..a91d453
--- /dev/null
+++ b/apps/testing-harness/tsconfig.json
@@ -0,0 +1,32 @@
+{
+  "compilerOptions": {
+    "target": "es2022",
+    "useDefineForClassFields": false,
+    "forceConsistentCasingInFileNames": true,
+    "strict": true,
+    "noImplicitOverride": true,
+    "noPropertyAccessFromIndexSignature": true,
+    "noImplicitReturns": true,
+    "noFallthroughCasesInSwitch": true
+  },
+  "files": [],
+  "include": [],
+  "references": [
+    {
+      "path": "./tsconfig.app.json"
+    },
+    {
+      "path": "./tsconfig.editor.json"
+    },
+    {
+      "path": "./tsconfig.spec.json"
+    }
+  ],
+  "extends": "../../tsconfig.base.json",
+  "angularCompilerOptions": {
+    "enableI18nLegacyMessageIdFormat": false,
+    "strictInjectionParameters": true,
+    "strictInputAccessModifiers": true,
+    "strictTemplates": true
+  }
+}
diff --git a/apps/testing-harness/tsconfig.spec.json b/apps/testing-harness/tsconfig.spec.json
new file mode 100644
index 0000000..6a6661c
--- /dev/null
+++ b/apps/testing-harness/tsconfig.spec.json
@@ -0,0 +1,16 @@
+{
+  "extends": "./tsconfig.json",
+  "compilerOptions": {
+    "outDir": "../../dist/out-tsc",
+    "module": "commonjs",
+    "target": "es2016",
+    "types": ["jest", "node", "@testing-library/jest-dom"]
+  },
+  "files": ["src/test-setup.ts"],
+  "include": [
+    "jest.config.ts",
+    "src/**/*.test.ts",
+    "src/**/*.spec.ts",
+    "src/**/*.d.ts"
+  ]
+}