Studio Testing

Patterns and practices for testing the TypeScript/React Studio.

Framework

• Vitest for test execution (Vite-native, fast)
• React Testing Library for component tests
• jsdom for DOM environment

Running Tests

cd studio

# All unit tests
bun run test

# Watch mode (re-runs on change)
bun run test:watch

# With coverage
bun run test:coverage

# Specific file
bun run test WorkflowSerializer

# Integration tests (requires Server)
bun run test:integration

Test Organization

studio/src/
|-- __tests__/
|   `-- type-contracts.test.ts      # Studio/Server contract tests
|-- domain/
|   `-- workflow/
|       `-- services/
|           `-- __tests__/
|               |-- WorkflowSerializer.test.ts
|               `-- loopDetection.test.ts
|-- state/
|   `-- __tests__/
|       |-- workflowStore.test.ts
|       |-- historyStore.test.ts
|       `-- store-integration.test.ts
|-- hooks/
|   `-- __tests__/
|       `-- useToolConfiguration.test.ts
|-- utils/
|   `-- __tests__/
|       |-- id.test.ts
|       `-- alignDistribute.test.ts
|-- components/
|   |-- __tests__/
|   |   |-- FilterConfiguration.test.tsx
|   |   `-- FormulaConfiguration.test.tsx
|   `-- primitives/
|       `-- __tests__/
|           |-- ConfigText.test.tsx
|           `-- ConfigSelect.test.tsx
`-- api/
    `-- __tests__/
        `-- backend.test.ts

Tests live next to what they test, in __tests__ directories.

Domain Logic Testing

Pure TypeScript, no React. These are the most valuable tests.

Serialization Tests

import { describe, it, expect } from 'vitest';
import { WorkflowSerializer } from '../WorkflowSerializer';
import { createTestTool, createTestWire } from '@/test-utils';

describe('WorkflowSerializer', () => {
  describe('toJSON', () => {
    it('serializes tools correctly', () => {
      const tools = [createTestTool('t1', 'Input')];
      const wires = [];
      const meta = createTestMeta();
      
      const json = WorkflowSerializer.toJSON(tools, wires, meta);
      const parsed = JSON.parse(json);
      
      expect(parsed.tools).toHaveLength(1);
      expect(parsed.tools[0].type).toBe('Input');
    });
    
    it('preserves wire connections', () => {
      const tools = [
        createTestTool('t1', 'Input'),
        createTestTool('t2', 'Filter'),
      ];
      const wires = [createTestWire('t1', 'output', 't2', 'input')];
      
      const json = WorkflowSerializer.toJSON(tools, wires, createTestMeta());
      const parsed = JSON.parse(json);
      
      expect(parsed.wires).toHaveLength(1);
      expect(parsed.wires[0].from.tool).toBe('t1');
    });
  });
  
  describe('fromJSON', () => {
    it('round-trips without data loss', () => {
      const original = {
        tools: [createTestTool('t1', 'Input')],
        wires: [],
        meta: createTestMeta(),
      };
      
      const json = WorkflowSerializer.toJSON(
        original.tools, 
        original.wires, 
        original.meta
      );
      const restored = WorkflowSerializer.fromJSON(json);
      
      expect(restored.tools).toEqual(original.tools);
    });
  });
});

Loop Detection Tests

import { describe, it, expect } from 'vitest';
import { wouldCreateCycle } from '../loopDetection';

describe('wouldCreateCycle', () => {
  it('returns false for valid connections', () => {
    const tools = [
      { id: 'a', ... },
      { id: 'b', ... },
    ];
    const wires = [];
    const newWire = { from: { tool: 'a' }, to: { tool: 'b' } };
    
    expect(wouldCreateCycle(tools, wires, newWire)).toBe(false);
  });
  
  it('returns true for direct cycle', () => {
    const tools = [
      { id: 'a', ... },
      { id: 'b', ... },
    ];
    const wires = [
      { from: { tool: 'a' }, to: { tool: 'b' } },
    ];
    const newWire = { from: { tool: 'b' }, to: { tool: 'a' } };
    
    expect(wouldCreateCycle(tools, wires, newWire)).toBe(true);
  });
  
  it('returns true for transitive cycle', () => {
    const tools = [
      { id: 'a', ... },
      { id: 'b', ... },
      { id: 'c', ... },
    ];
    const wires = [
      { from: { tool: 'a' }, to: { tool: 'b' } },
      { from: { tool: 'b' }, to: { tool: 'c' } },
    ];
    const newWire = { from: { tool: 'c' }, to: { tool: 'a' } };
    
    expect(wouldCreateCycle(tools, wires, newWire)).toBe(true);
  });
});

State Store Testing

Testing Zustand stores directly:

import { describe, it, expect, beforeEach } from 'vitest';
import { useWorkflowStore } from '../workflowStore';
import { createTestTool, createTestWire } from '@/test-utils';

describe('workflowStore', () => {
  beforeEach(() => {
    // Reset store between tests
    useWorkflowStore.getState().clear();
  });
  
  describe('addTool', () => {
    it('adds tool to state', () => {
      const tool = createTestTool('t1', 'Input');
      
      useWorkflowStore.getState().addTool(tool);
      
      const { tools } = useWorkflowStore.getState();
      expect(tools).toHaveLength(1);
      expect(tools[0].id).toBe('t1');
    });
  });
  
  describe('addWire', () => {
    it('creates valid connection', () => {
      const t1 = createTestTool('t1', 'Input');
      const t2 = createTestTool('t2', 'Filter');
      useWorkflowStore.getState().addTool(t1);
      useWorkflowStore.getState().addTool(t2);
      
      const result = useWorkflowStore.getState().addWire({
        from: { tool: 't1', socket: 'output' },
        to: { tool: 't2', socket: 'input' },
      });
      
      expect(result.success).toBe(true);
      expect(useWorkflowStore.getState().wires).toHaveLength(1);
    });
    
    it('rejects cycle-creating connection', () => {
      // Setup: t1 -> t2
      // Attempt: t2 -> t1 (would create cycle)
      
      const result = useWorkflowStore.getState().addWire({
        from: { tool: 't2', socket: 'output' },
        to: { tool: 't1', socket: 'input' },
      });
      
      expect(result.success).toBe(false);
      expect(result.error).toContain('cycle');
    });
  });
  
  describe('updateToolConfiguration', () => {
    it('updates config immutably', () => {
      const tool = createTestTool('t1', 'Filter', { expression: '' });
      useWorkflowStore.getState().addTool(tool);
      
      useWorkflowStore.getState().updateToolConfiguration('t1', {
        expression: 'age > 30',
      });
      
      const updated = useWorkflowStore.getState().tools[0];
      expect(updated.config.expression).toBe('age > 30');
      
      // Original unchanged (immutability)
      expect(tool.config.expression).toBe('');
    });
  });
});

History Store Tests

describe('historyStore', () => {
  beforeEach(() => {
    useHistoryStore.getState().clear();
  });
  
  it('tracks state changes', () => {
    const state1 = createSnapshot([]);
    const state2 = createSnapshot([createTestTool()]);
    
    useHistoryStore.getState().pushState(state1);
    useHistoryStore.getState().pushState(state2);
    
    expect(useHistoryStore.getState().canUndo()).toBe(true);
  });
  
  it('undoes to previous state', () => {
    const tool = createTestTool();
    useHistoryStore.getState().pushState(createSnapshot([]));
    useHistoryStore.getState().pushState(createSnapshot([tool]));
    
    const restored = useHistoryStore.getState().undo();
    
    expect(restored.tools).toHaveLength(0);
  });
  
  it('limits history size', () => {
    for (let i = 0; i < 100; i++) {
      useHistoryStore.getState().pushState(createSnapshot([]));
    }
    
    // Should cap at max size (e.g., 50)
    expect(useHistoryStore.getState().past.length).toBeLessThanOrEqual(50);
  });
});

Hook Testing

useToolConfiguration Tests

The useToolConfiguration hook is tested with React Testing Library's renderHook:

import { describe, it, expect, vi, beforeEach } from 'vitest';
import { renderHook, act, waitFor } from '@testing-library/react';
import { useToolConfiguration } from '../useToolConfiguration';
import { CommonSockets } from '@domain/workflow/constants/socketIds';

describe('useToolConfiguration', () => {
  const mockOnChange = vi.fn();
  
  beforeEach(() => {
    mockOnChange.mockClear();
  });
  
  it('detects connected inputs', () => {
    const tools = [createTestTool('input', 'Input'), createTestTool('filter', 'Filter')];
    const wires = [createTestWire('input', 'output', 'filter', 'input')];
    
    const { result } = renderHook(() => useToolConfiguration({
      toolId: 'filter',
      socketId: CommonSockets.INPUT,
      tools,
      wires,
      workflowMeta: createTestMeta(),
      config: {},
      onChange: mockOnChange,
    }));
    
    expect(result.current.hasInput).toBe(true);
  });
  
  it('generates stable connectionKey', () => {
    const wires = [createTestWire('a', 'output', 'target', 'input')];
    
    const { result, rerender } = renderHook(() => useToolConfiguration({...}));
    const key1 = result.current.connectionKey;
    
    rerender();
    
    expect(result.current.connectionKey).toBe(key1);
  });
  
  it('refetches metadata when connections change', async () => {
    const fetchMetadata = vi.fn();
    vi.mock('../api/hooks', () => ({
      useMetadata: () => ({
        columns: [],
        loading: false,
        error: null,
        fetchMetadata,
      }),
    }));
    
    const wires1 = [createTestWire('a', 'output', 'target', 'input')];
    const wires2 = [createTestWire('b', 'output', 'target', 'input')];
    
    const { rerender } = renderHook(
      ({ wires }) => useToolConfiguration({ toolId: 'target', wires, ... }),
      { initialProps: { wires: wires1 } }
    );
    
    await waitFor(() => expect(fetchMetadata).toHaveBeenCalledTimes(1));
    
    rerender({ wires: wires2 });
    
    await waitFor(() => expect(fetchMetadata).toHaveBeenCalledTimes(2));
  });
  
  it('updateField tracks emission', () => {
    const { result } = renderHook(() => useToolConfiguration({
      config: { expression: '' },
      onChange: mockOnChange,
      ...
    }));
    
    act(() => {
      result.current.updateField('expression', 'age > 30');
    });
    
    expect(mockOnChange).toHaveBeenCalledWith(
      expect.objectContaining({
        expression: 'age > 30',
        _emit: { expression: true },
      })
    );
  });
});

Type Contract Testing

Type contract tests validate that frontend and backend stay in sync.

Socket ID Contracts

// src/__tests__/type-contracts.test.ts
import { describe, it, expect } from 'vitest';
import { CommonSockets, FilterSockets, JoinSockets } from '@domain/workflow/constants/socketIds';
import { TOOL_DEFINITIONS } from '@/data/tools';

describe('Socket ID Contracts', () => {
  it('Filter tool uses correct socket IDs', () => {
    const filterDef = TOOL_DEFINITIONS.find(t => t.type === 'Filter')!;
    const socketIds = filterDef.sockets.map(s => s.id);
    
    expect(socketIds).toContain(FilterSockets.INPUT);
    expect(socketIds).toContain(FilterSockets.OUTPUT_TRUE);
    expect(socketIds).toContain(FilterSockets.OUTPUT_FALSE);
  });
  
  it('Join tool uses correct socket IDs', () => {
    const joinDef = TOOL_DEFINITIONS.find(t => t.type === 'Join')!;
    const socketIds = joinDef.sockets.map(s => s.id);
    
    expect(socketIds).toContain(JoinSockets.INPUT_LEFT);
    expect(socketIds).toContain(JoinSockets.INPUT_RIGHT);
    expect(socketIds).toContain(JoinSockets.OUTPUT_LEFT);
    expect(socketIds).toContain(JoinSockets.OUTPUT_MATCH);
    expect(socketIds).toContain(JoinSockets.OUTPUT_RIGHT);
  });
});

Workflow Serialization Contracts

describe('Workflow Serialization Contracts', () => {
  it('produces valid workflow JSON for backend', () => {
    const tools = [
      createTestTool('input', 'Input', { path: '/data/test.csv' }),
      createTestTool('filter', 'Filter', { expression: 'age > 30' }),
    ];
    const wires = [createTestWire('input', 'output', 'filter', 'input')];
    
    const json = WorkflowSerializer.toJSON(tools, wires, createTestMeta());
    const workflow = JSON.parse(json);
    
    // Validate structure matches backend Pydantic models
    expect(workflow).toHaveProperty('version');
    expect(workflow).toHaveProperty('meta.workflow_id');
    expect(workflow).toHaveProperty('tools');
    expect(workflow).toHaveProperty('wires');
    
    // Tools have required fields
    for (const tool of workflow.tools) {
      expect(tool).toHaveProperty('id');
      expect(tool).toHaveProperty('type');
      expect(tool).toHaveProperty('config');
      expect(tool).toHaveProperty('sockets');
      expect(tool).toHaveProperty('position');
    }
    
    // Wires have required fields
    for (const wire of workflow.wires) {
      expect(wire).toHaveProperty('from.tool');
      expect(wire).toHaveProperty('from.socket');
      expect(wire).toHaveProperty('to.tool');
      expect(wire).toHaveProperty('to.socket');
    }
  });
});

These tests ensure that changes to either frontend or backend serialization formats are caught before they cause runtime errors.

Component Testing

Light coverage for components. Focus on behavior, not rendering.

import { render, screen, fireEvent } from '@testing-library/react';
import { describe, it, expect, vi } from 'vitest';
import { ConfigText } from '../ConfigText';

describe('ConfigText', () => {
  it('renders current value', () => {
    render(<ConfigText value="hello" onChange={() => {}} />);
    
    expect(screen.getByRole('textbox')).toHaveValue('hello');
  });
  
  it('calls onChange when input changes', () => {
    const onChange = vi.fn();
    render(<ConfigText value="" onChange={onChange} />);
    
    fireEvent.change(screen.getByRole('textbox'), {
      target: { value: 'new value' },
    });
    
    expect(onChange).toHaveBeenCalledWith('new value', expect.anything(), true);
  });
  
  it('shows validation error', () => {
    render(
      <ConfigText 
        value="" 
        onChange={() => {}} 
        required 
        errorMessage="Field is required"
      />
    );
    
    expect(screen.getByText('Field is required')).toBeInTheDocument();
  });
});

Testing with Store Dependencies

Mock the store:

import { vi } from 'vitest';

vi.mock('@/state/workflowStore', () => ({
  useWorkflowStore: vi.fn((selector) => 
    selector({
      tools: [],
      wires: [],
      selectedTool: null,
      addTool: vi.fn(),
    })
  ),
}));

Or provide test values:

import { useWorkflowStore } from '@/state/workflowStore';

beforeEach(() => {
  useWorkflowStore.setState({
    tools: [createTestTool()],
    wires: [],
  });
});

Test Utilities

Create helpers for common patterns:

// test-utils.ts

export function createTestTool(
  id = 'test-tool',
  type = 'Input',
  config = {},
): Tool {
  return {
    id,
    type,
    x: 0,
    y: 0,
    config,
    sockets: getDefaultSockets(type),
  };
}

export function createTestWire(
  fromTool: string,
  fromSocket: string,
  toTool: string,
  toSocket: string,
): Wire {
  return {
    from: { tool: fromTool, socket: fromSocket },
    to: { tool: toTool, socket: toSocket },
  };
}

export function createTestMeta(): WorkflowMeta {
  return {
    name: 'Test Workflow',
    description: '',
    author: 'Test',
    workflowId: 'test-id',
    created: new Date().toISOString(),
  };
}

What Not to Test

// Don't test implementation details
it('sets internal state to X')  // Bad

// Don't test CSS classes
expect(element).toHaveClass('bg-blue-500')  // Bad - brittle

// Don't snapshot test frequently-changing UI
expect(component).toMatchSnapshot()  // Bad - constant updates

// Don't test third-party libraries
it('React Flow renders nodes')  // Their problem, not ours

Integration Tests

For testing frontend + backend together:

// test:integration script starts backend first

describe('API Integration', () => {
  it('fetches schema from backend', async () => {
    const workflow = createTestWorkflow();
    
      const response = await fetch('/api/workflow/tool/schema', {
      method: 'POST',
      body: JSON.stringify({ tool_id: 'filter', workflow }),
    });
    
    expect(response.ok).toBe(true);
    const data = await response.json();
    expect(data.columns).toBeDefined();
  });
});

Run with:

bun run test:integration

This starts the backend, runs integration tests, then stops the backend.

---

Next: Integration Testing for end-to-end testing approach.