wip

[midleman]

POC (experiment)

Improves the Positron unit test experience with three changes:

1. A builder pattern that simplifies test setup from 2,500 lines of service wiring to a one-liner (createTestContainer().withRuntimeServices().build())
2. A /unit-tests-author slash command that analyzes your branch or PR, recommends tests by tier, and writes them after approval
3. Vitest migration (seeking feedback) -- watch mode, cleaner syntax, no build daemons needed. All 67 Positron test files migrated, 1,016 tests passing.

Why

Writing Positron unit tests required deep knowledge of VS Code's DI system, 124+ service stubs, and background build daemons. This friction led to 20+ Positron modules with zero unit tests and heavy reliance on E2E tests.

The Builder Pattern

createTestContainer() provides tiered presets for common service groupings. Pick the lowest one that works:

Preset	What it provides
Bare	Empty container -- for pure logic tests
Runtime	Language runtime + session services (~18 pre-configured)
Notebooks	Runtime + notebook/kernel services
Workbench	Full Positron stack (124+ services)

Any preset can override or add individual services with .stub(IService, mock). New presets are easy to add -- the Notebooks one was ~25 lines.

Example (Runtime):

import { createTestContainer } from '../../test/browser/positronTestContainer.js';

describe('MyRuntimeFeature', () => {
    const ctx = createTestContainer().withRuntimeServices().build();

    it('starts a session', async () => {
        const session = await startTestLanguageRuntimeSession(ctx.instantiationService, ctx.disposables);
        expect(session).toBeDefined();
    });
});

What changed

New infrastructure files:

File	Purpose
vitest.config.ts + tsconfig.vitest.json	Vitest runner config with separate TypeScript config to avoid Mocha type conflicts
src/vs/workbench/test/browser/positronTestContainer.ts	Builder pattern (createTestContainer()) with tiered presets (see above)
src/vs/base/test/common/vitestSetup.ts	Vitest-compatible disposable lifecycle tracking
src/vs/base/test/browser/reactVitest.tsx	Vitest-compatible React renderer (replaces Mocha's setupReactRenderer())
scripts/test-positron-vitest.sh	Convenience script for running Vitest
Stubs: vscode-stub.ts, positron-stub.ts, vscode-languageclient-stub.ts, p-queue-stub.ts, split2-stub.ts, git-api-stub.ts	Lightweight module stubs for extension tests with transitive VS Code dependencies

Modified infrastructure files:

File	Change
package.json	Added vitest, @vitest/coverage-v8, happy-dom, @testing-library/react devDependencies and test-vitest/test-vitest:run/test-vitest:coverage scripts
src/tsconfig.json	Exclude .vitest.ts files from main compilation
extensions/positron-assistant/tsconfig.json, extensions/positron-r/tsconfig.json	Exclude .vitest.ts from extension compilation
build/lib/compilation.ts	Exclude .vitest.ts from gulp compile, transpile, and watch tasks
.github/workflows/test-unit.yml	Added Vitest CI step (runs before compilation, ~2 min)
CLAUDE.md	Testing pyramid decision tree, tier guide, incremental mocking guide
.claude/commands/unit-tests-author.md	/unit-tests-author slash command for analyzing branches/PRs and writing tests

Tests migrated from Mocha to Vitest (67 core files):

All Positron-specific .test.ts files in src/vs/ were migrated to .vitest.ts. The originals were deleted. Changes per file:

• suite() -> describe(), test() -> it(), assert.* -> expect().*
• ensureNoDisposablesAreLeakedInTestSuite() replaced by builder's automatic lifecycle management
• positronWorkbenchInstantiationService() / createRuntimeServices() replaced by createTestContainer() builder

Tests extracted from extension host to Vitest (8 files):

Pure logic tests that were running through the full Electron extension host (20-30s startup) now run in Vitest (~200ms):

• positron-assistant: snowflake, autoconfiguredProviders, openai-fetch-utils, anthropicVercel, awsBedrock, notebookContextFilter
• positron-r: hyperlink, rversions

New test coverage:

• quartoKernelManager.vitest.ts -- 5 new tests for Quarto kernel lifecycle management (previously untested)
• runtimeSession.vitest.ts -- 6 new tests for session tracking (getLastActiveConsoleSession, removeNotebookSessionFromNotebookMap, selectRuntime exited session cleanup)

/unit-tests-author slash command:

Analyzes a branch diff or PR, classifies changed files by tier, and writes tests after approval:

/unit-tests-author                    # current branch
/unit-tests-author 12593              # PR number
/unit-tests-author --branch my-branch # specific branch

The command shows its reasoning for each tier recommendation, so devs learn the system as they use it. The 11 new tests above were produced by running /unit-tests-author 12593.

What did NOT change

• Upstream VS Code tests -- all 814 .test.ts files stay on Mocha, untouched
• E2E tests -- Playwright infrastructure unaffected
• Extension host tests -- npm run test-extension pipeline unchanged
• Build system -- daemons, compilation, packaging unchanged

Developer workflow

Before (Mocha):

1. Edit code
2. ./scripts/test.sh --run src/path/to/file.test.ts
3. Read results, repeat

Devs typically already have build daemons running for the app, so compilation isn't extra friction per test run. The main friction: no watch mode (manual re-run after each change).

After (Vitest):

1. npm run test-vitest    (starts watch mode, one-time)
2. Edit code
3. Results appear on save

Watch mode is the key improvement -- tests re-run automatically. Vitest also doesn't need build daemons at all, which matters for CI and for running tests without launching the full app.

Numbers

Metric	Value
Vitest test files	76
Tests passing	1,016
Vitest CI step	~2 minutes (no Electron/xvfb/compilation)
New test coverage	11 tests across 2 previously untested areas

Test plan

• npm run test-vitest:run -- all 1,016 tests pass locally
• CI unit test job passes (Vitest step + upstream Mocha steps)
• CI integration test job passes (extension compilation excludes .vitest.ts)
• CI e2e test job passes
• Verify watch mode works: npm run test-vitest, edit a .vitest.ts file, confirm re-run
• Verify upstream tests unaffected: npm run build-start && npm run build-check && ./scripts/test-positron.sh

🤖 Generated with Claude Code

[github-actions]

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