tests: add Playwright E2E tests with screenshot golden testing (+ fix examples session handling) (#115)

* Add Playwright E2E tests with screenshot golden testing

- Add E2E tests for all 8 MCP server examples
- Screenshot golden images for visual regression testing
- CI workflow for running E2E tests
- npm scripts: test:e2e, test:e2e:update, test:e2e:ui

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Co-Authored-By: Claude <noreply@anthropic.com>

* Add default demo code for Three.js example

When no code is provided, show a rotating green cube demo.

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Co-Authored-By: Claude <noreply@anthropic.com>

* Add E2E testing documentation to CONTRIBUTING.md

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Co-Authored-By: Claude <noreply@anthropic.com>

* Update Three.js golden screenshot with 3D cube

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* Add explicit permissions to CI workflow

Set minimal read-only permissions for security best practices.

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Co-Authored-By: Claude <noreply@anthropic.com>

* Fix test.setTimeout() to be inside describe blocks

Playwright requires setTimeout to be called within a test or describe block.

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Co-Authored-By: Claude <noreply@anthropic.com>

* Simplify E2E tests - remove excessive timeouts

- Remove explicit setTimeout calls (default 30s is sufficient)
- Replace waitForTimeout(5000/6000) with proper waitForAppLoad()
- Wait for inner iframe visibility instead of fixed delays
- Keep only 500ms stabilization for screenshot animations

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* Auto-generate missing snapshots in CI

Use updateSnapshots: 'missing' in CI to handle cross-platform
screenshot differences (macOS vs Linux).

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Co-Authored-By: Claude <noreply@anthropic.com>

* Use platform-agnostic golden screenshots

- Remove -chromium-darwin suffix from snapshot filenames
- Configure snapshotPathTemplate for cross-platform compatibility
- Increase tolerance to 5% for rendering differences between platforms

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* Refactor tests to use forEach instead of for-of loop

May help with Playwright test discovery issues in CI.

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Co-Authored-By: Claude <noreply@anthropic.com>

* Use npm ci and list reporter in CI

- Use npm ci for exact package versions
- Use --reporter=list instead of html to avoid potential re-evaluation issues
- Only upload test-results on failure

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* Exclude e2e tests from bun test

Run bun test only on src/ directory to avoid running Playwright tests
with Bun's test runner.

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* Fix prettier formatting

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* Add interaction tests for basic server apps

Test that clicking buttons in the MCP App triggers the corresponding
host callbacks:
- Send Message → host logs "Message from MCP App"
- Send Log → host logs "Log message from MCP App"
- Open Link → host logs "Open link request"

Tests both React and Vanilla JS implementations.

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* Mask dynamic content in E2E screenshot tests

Add Playwright mask option to handle servers with dynamic/random content:
- basic-react/vanillajs: mask server time display
- system-monitor: mask CPU chart, memory stats, uptime
- cohort-heatmap: mask heatmap grid (random data)
- customer-segmentation: mask scatter chart (random data)

This addresses PR feedback about handling examples with non-deterministic
output. Masking replaces the previous 10% tolerance with proper exclusion
of dynamic elements, allowing tighter 1% tolerance for the rest of the UI.

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Co-Authored-By: Claude <noreply@anthropic.com>

* Add wiki-explorer to E2E tests with default URL param

- Add default URL "https://en.wikipedia.org/wiki/Model_Context_Protocol" to
  wiki-explorer-server's get-first-degree-links tool inputSchema
- Update basic-host to automatically populate input field with tool defaults
  extracted from inputSchema.properties
- Add wiki-explorer-server to E2E test suite with dynamic masking for the
  force-directed graph

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Co-Authored-By: Claude <noreply@anthropic.com>

* Use .default() for threejs tool schema instead of .optional()

This exposes the default code and height values in the JSON Schema,
allowing basic-host to auto-populate the input field with defaults.

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* Enable parallel E2E tests with timeouts and canvas masking

- Enable fullyParallel with 4 workers locally (2 in CI)
- Add 30s timeout per test
- Mask threejs canvas for stable screenshots
- Update snapshots to reflect default values in input fields

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* Add pre-commit check for private registry URLs in package-lock.json

Same check as in CI to catch issues before push.

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Co-Authored-By: Claude <noreply@anthropic.com>

* Increase screenshot diff tolerance to 6% for cross-platform rendering

Font rendering differs between macOS and Linux, causing ~5% pixel differences.

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Co-Authored-By: Claude <noreply@anthropic.com>

* Revert pre-commit artifactory check (moved to separate PR #133)

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* Format threejs server.ts

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* Update CONTRIBUTING.md to reflect platform-agnostic screenshots

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* fix(e2e): use factory pattern for MCP servers to support parallel connections

McpServer only supports one transport at a time. When multiple browser
contexts connected in parallel, calling server.connect(transport) for
each session overwrote the previous transport's callbacks, causing
connection corruption and test timeouts.

Changes:
- server-utils.ts: accept factory function instead of single instance
- All 9 example servers: wrap server creation in createServer() function
- playwright.config.ts: re-enable parallel execution (4 workers)
- servers.spec.ts: add toBeEnabled wait for server connection
- Update screenshot baselines for basic-vanillajs and cohort-heatmap

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -6,6 +6,9 @@ on:
   pull_request:
     branches: [main]
 
+permissions:
+  contents: read
+
 jobs:
   build:
     runs-on: ubuntu-latest
@@ -35,3 +38,32 @@ jobs:
       - run: npm test
 
       - run: npm run prettier
+
+  e2e:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: oven-sh/setup-bun@v2
+        with:
+          bun-version: latest
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: "20"
+
+      - run: npm ci
+
+      - name: Install Playwright browsers
+        run: npx playwright install --with-deps chromium
+
+      - name: Run E2E tests
+        run: npx playwright test --reporter=list
+
+      - name: Upload test results
+        uses: actions/upload-artifact@v4
+        if: failure()
+        with:
+          name: test-results
+          path: test-results/
+          retention-days: 7