Redux Debugging & Testing

Debugging and testing Redux state in MistWarp requires understanding the store structure, using development tools effectively, and implementing comprehensive test coverage.

Development Tools

Redux DevTools

Access Redux DevTools through browser extensions:

// Store setup with DevTools
const configureStore = (initialState) => {
  const composeEnhancers = 
    window.__REDUX_DEVTOOLS_EXTENSION_COMPOSE__ || compose;
  
  return createStore(
    rootReducer,
    initialState,
    composeEnhancers(applyMiddleware(thunk))
  );
};

DevTools features:

• Time Travel: Step through action history
• State Inspection: View current and historical state
• Action Replay: Replay actions from any point
• State Import/Export: Save and load state snapshots

Browser Console Debugging

Add debugging helpers to window object:

// Add to browser console for debugging
window.inspectReduxState = () => {
  const state = store.getState();
  console.log('Redux State:', state);
  return state;
};

window.dispatchAction = (action) => {
  store.dispatch(action);
  console.log('Dispatched:', action);
};

// Inspect specific state slices
window.getProjectState = () => store.getState().projectState;
window.getVMState = () => store.getState().vm;
window.getGUIState = () => store.getState().gui;

State Inspection Utilities

// Development utilities
const createStateInspector = (store) => {
  return {
    // Get current state
    getState: () => store.getState(),
    
    // Get specific slice
    getSlice: (path) => {
      const state = store.getState();
      return path.split('.').reduce((obj, key) => obj?.[key], state);
    },
    
    // Find state by predicate
    findInState: (predicate, obj = store.getState(), path = '') => {
      const results = [];
      
      Object.entries(obj).forEach(([key, value]) => {
        const currentPath = path ? `${path}.${key}` : key;
        
        if (predicate(value, key, currentPath)) {
          results.push({ path: currentPath, value });
        }
        
        if (typeof value === 'object' && value !== null) {
          results.push(...this.findInState(predicate, value, currentPath));
        }
      });
      
      return results;
    },
    
    // Monitor state changes
    watchState: (path, callback) => {
      let lastValue = this.getSlice(path);
      
      return store.subscribe(() => {
        const currentValue = this.getSlice(path);
        if (currentValue !== lastValue) {
          callback(currentValue, lastValue);
          lastValue = currentValue;
        }
      });
    }
  };
};

// Usage
const inspector = createStateInspector(store);
inspector.watchState('projectState.saveState', (current, previous) => {
  console.log(`Save state changed: ${previous} → ${current}`);
});

Testing Strategies

Reducer Testing

Test reducers in isolation:

import projectStateReducer from '../reducers/project-state';

describe('projectStateReducer', () => {
  const initialState = {
    projectId: null,
    projectTitle: '',
    isLoading: false,
    error: null,
    saveState: 'NOT_SAVED'
  };
  
  test('should handle SET_PROJECT_ID', () => {
    const action = { type: 'SET_PROJECT_ID', projectId: '123456789' };
    const newState = projectStateReducer(initialState, action);
    
    expect(newState.projectId).toBe('123456789');
    expect(newState).not.toBe(initialState); // Immutability check
  });
  
  test('should handle SET_PROJECT_LOADING', () => {
    const stateWithError = { ...initialState, error: 'Previous error' };
    const action = { type: 'SET_PROJECT_LOADING', isLoading: true };
    const newState = projectStateReducer(stateWithError, action);
    
    expect(newState.isLoading).toBe(true);
    expect(newState.error).toBe(null); // Error should be cleared
  });
  
  test('should return current state for unknown actions', () => {
    const action = { type: 'UNKNOWN_ACTION' };
    const newState = projectStateReducer(initialState, action);
    
    expect(newState).toBe(initialState);
  });
});

Action Creator Testing

import { setProjectTitle, loadProject } from '../actions/project-actions';

describe('Project Actions', () => {
  test('setProjectTitle should create correct action', () => {
    const title = 'My Project';
    const expectedAction = {
      type: 'SET_PROJECT_TITLE',
      title
    };
    
    expect(setProjectTitle(title)).toEqual(expectedAction);
  });
  
  test('loadProject should handle async loading', async () => {
    const mockDispatch = jest.fn();
    const mockGetState = jest.fn();
    
    // Mock fetch
    global.fetch = jest.fn(() =>
      Promise.resolve({
        json: () => Promise.resolve({ id: '123', title: 'Test Project' })
      })
    );
    
    const thunk = loadProject('123');
    await thunk(mockDispatch, mockGetState);
    
    expect(mockDispatch).toHaveBeenCalledWith({
      type: 'SET_PROJECT_LOADING',
      isLoading: true
    });
    
    expect(mockDispatch).toHaveBeenCalledWith({
      type: 'SET_PROJECT',
      project: { id: '123', title: 'Test Project' }
    });
  });
});

Store Integration Testing

Test complete store behavior:

import configureStore from '../store';

describe('Redux Store Integration', () => {
  let store;
  
  beforeEach(() => {
    store = configureStore();
  });
  
  test('should initialize with correct default state', () => {
    const state = store.getState();
    
    expect(state.projectState.projectId).toBe(null);
    expect(state.gui.theme.theme).toBe('light');
    expect(state.vm.targets).toEqual([]);
  });
  
  test('should handle action dispatch workflow', () => {
    // Set project ID
    store.dispatch({
      type: 'SET_PROJECT_ID',
      projectId: '123456789'
    });
    
    let state = store.getState();
    expect(state.projectState.projectId).toBe('123456789');
    
    // Set project title
    store.dispatch({
      type: 'SET_PROJECT_TITLE',
      title: 'My Project'
    });
    
    state = store.getState();
    expect(state.projectState.projectTitle).toBe('My Project');
  });
  
  test('should handle multiple state updates', () => {
    const actions = [
      { type: 'SET_PROJECT_ID', projectId: '123' },
      { type: 'SET_PROJECT_TITLE', title: 'Test' },
      { type: 'SET_THEME', theme: 'dark' },
      { type: 'SET_STAGE_SIZE', stageSize: 'small' }
    ];
    
    actions.forEach(action => store.dispatch(action));
    
    const state = store.getState();
    expect(state.projectState.projectId).toBe('123');
    expect(state.projectState.projectTitle).toBe('Test');
    expect(state.gui.theme.theme).toBe('dark');
    expect(state.gui.stage.stageSize).toBe('small');
  });
});

Selector Testing

import { 
  getProjectStatus, 
  getIsProjectLoaded, 
  getSpriteCount 
} from '../selectors';

describe('Selectors', () => {
  const mockState = {
    projectState: {
      projectId: '123',
      isLoading: false,
      saveState: 'NOT_SAVED'
    },
    vm: {
      targets: [
        { id: 'stage', isStage: true },
        { id: 'sprite1', isStage: false },
        { id: 'sprite2', isStage: false }
      ]
    }
  };
  
  test('getIsProjectLoaded should return correct value', () => {
    expect(getIsProjectLoaded(mockState)).toBe(true);
    
    const loadingState = {
      ...mockState,
      projectState: { ...mockState.projectState, isLoading: true }
    };
    expect(getIsProjectLoaded(loadingState)).toBe(false);
  });
  
  test('getProjectStatus should return correct status', () => {
    expect(getProjectStatus(mockState)).toBe('unsaved');
    
    const savedState = {
      ...mockState,
      projectState: { ...mockState.projectState, saveState: 'SAVED' }
    };
    expect(getProjectStatus(savedState)).toBe('saved');
  });
  
  test('getSpriteCount should count non-stage targets', () => {
    expect(getSpriteCount(mockState)).toBe(2);
  });
});

Error Debugging

Error Boundary for Redux

class ReduxErrorBoundary extends React.Component {
  constructor(props) {
    super(props);
    this.state = { hasError: false, error: null };
  }
  
  static getDerivedStateFromError(error) {
    return { hasError: true, error };
  }
  
  componentDidCatch(error, errorInfo) {
    console.error('Redux Error:', error);
    console.error('Error Info:', errorInfo);
    
    // Log to error tracking service
    if (window.errorTracker) {
      window.errorTracker.captureException(error, {
        context: 'Redux State',
        extra: errorInfo
      });
    }
  }
  
  render() {
    if (this.state.hasError) {
      return (
        <div className="error-boundary">
          <h2>Something went wrong with the application state</h2>
          <details>
            <summary>Error Details</summary>
            <pre>{this.state.error?.stack}</pre>
          </details>
          <button onClick={() => window.location.reload()}>
            Reload Application
          </button>
        </div>
      );
    }
    
    return this.props.children;
  }
}

State Validation

// State shape validation
const validateState = (state) => {
  const errors = [];
  
  // Validate project state
  if (state.projectState.projectId && typeof state.projectState.projectId !== 'string') {
    errors.push('projectState.projectId must be string or null');
  }
  
  // Validate VM state
  if (!Array.isArray(state.vm.targets)) {
    errors.push('vm.targets must be an array');
  }
  
  // Validate GUI state
  const validThemes = ['light', 'dark', 'high-contrast'];
  if (!validThemes.includes(state.gui.theme.theme)) {
    errors.push(`gui.theme.theme must be one of: ${validThemes.join(', ')}`);
  }
  
  return errors;
};

// Use in development
if (process.env.NODE_ENV === 'development') {
  store.subscribe(() => {
    const errors = validateState(store.getState());
    if (errors.length > 0) {
      console.error('State validation errors:', errors);
    }
  });
}

Performance Debugging

Action Performance Monitoring

const performanceDebugger = (store) => {
  const actionTimes = new Map();
  const slowActions = [];
  
  return {
    startTimer: (actionType) => {
      actionTimes.set(actionType, performance.now());
    },
    
    endTimer: (actionType) => {
      const startTime = actionTimes.get(actionType);
      if (startTime) {
        const duration = performance.now() - startTime;
        actionTimes.delete(actionType);
        
        if (duration > 10) {
          slowActions.push({ action: actionType, duration });
          console.warn(`Slow action: ${actionType} took ${duration.toFixed(2)}ms`);
        }
        
        return duration;
      }
    },
    
    getSlowActions: () => slowActions,
    
    reset: () => {
      actionTimes.clear();
      slowActions.length = 0;
    }
  };
};

Memory Usage Tracking

const memoryTracker = (store) => {
  const measurements = [];
  
  return {
    measure: (label) => {
      const state = store.getState();
      const stateSize = JSON.stringify(state).length;
      
      measurements.push({
        label,
        timestamp: Date.now(),
        stateSize,
        heapUsed: performance.memory?.usedJSHeapSize || 0
      });
    },
    
    getReport: () => {
      return measurements.map((m, i) => {
        const prev = measurements[i - 1];
        return {
          ...m,
          stateDelta: prev ? m.stateSize - prev.stateSize : 0,
          heapDelta: prev ? m.heapUsed - prev.heapUsed : 0
        };
      });
    }
  };
};

Debugging Common Issues

State Not Updating

// Check if reducer is handling action
const debugReducer = (reducer) => (state, action) => {
  console.log(`Reducer called with action: ${action.type}`);
  console.log('Previous state:', state);
  
  const newState = reducer(state, action);
  
  console.log('New state:', newState);
  console.log('State changed:', newState !== state);
  
  return newState;
};

Action Not Dispatching

// Wrap dispatch to debug
const debugDispatch = (originalDispatch) => (action) => {
  console.log('Dispatching action:', action);
  
  try {
    const result = originalDispatch(action);
    console.log('Action dispatched successfully');
    return result;
  } catch (error) {
    console.error('Error dispatching action:', error);
    throw error;
  }
};

store.dispatch = debugDispatch(store.dispatch);

Component Not Re-rendering

// Debug useSelector
const useDebugSelector = (selector, equalityFn) => {
  const selected = useSelector(selector, equalityFn);
  
  useEffect(() => {
    console.log('Selector result changed:', selected);
  }, [selected]);
  
  return selected;
};

Redux debugging in MistWarp requires systematic approaches to testing, monitoring, and error handling to ensure reliable state management across the application.