Research-Stack/5-Applications/nodupe/wiki/Testing/Guide.md

Testing Guide

Last Updated: 2026-02-22 Status: ✅ Complete - 100% Project Completeness

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Quick Start

Running Tests

# Run all tests
pytest tests/ -v

# Run with coverage
pytest --cov=nodupe tests/

# Run specific test file
pytest tests/parallel/test_parallel_thread_vs_process.py -v

Coverage Reports

# HTML report
pytest --cov=nodupe --cov-report=html tests/
xdg-open htmlcov/index.html

# Terminal report with missing lines
pytest --cov=nodupe --cov-report=term-missing tests/

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Test Organization

tests/
├── archive/              # Archive tool tests
├── commands/             # Command tool tests
├── core/                 # Core module tests
├── database/             # Database tests
├── hashing/              # Hashing tests
├── leap_year/            # Leap year tool tests
├── maintenance/          # Maintenance tool tests
├── mime/                 # MIME detection tests
├── ml/                   # ML plugin tests
├── parallel/             # Parallel processing tests
├── plugins/              # Plugin system tests
├── scanner_engine/       # Scanner engine tests
├── security_audit/       # Security audit tests
├── time_sync/            # Time sync tests
└── test_*.py             # Cross-module tests

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Test Statistics

Metric	Value	Status
Total Tests	6,500+	✅ Active
Passing Tests	6,500+	✅ 100%
Failing Tests	0	✅ None
Line Coverage	93.30%	✅ Excellent
Branch Coverage	86.17%	✅ Excellent
Files at 100%	50+	✅ Complete

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Parallel Testing

Overview

The NoDupeLabs project uses a pickle-safe test helpers approach for testing parallel code that utilizes ProcessPoolExecutor.

Why Pickle-Safe Helpers?

• ✅ Tests REAL ProcessPoolExecutor (not mocks)
• ✅ More direct and explicit
• ✅ Better performance (no DI overhead)
• ✅ Already working perfectly (70+ tests passing)
• ✅ More maintainable long-term

Why NOT Dependency Injection?

• ❌ Static methods - Parallel is a utility class
• ❌ Direct executor instantiation - Clearer than abstraction
• ❌ Tests verify reality - Mocks don't test actual multiprocessing
• ❌ Performance - DI adds unnecessary overhead
• ❌ Complexity - Over-engineers simple utilities

See: PARALLEL_TESTING_GUIDE.md for complete details.

Test Helpers

Location: tests/parallel/test_helpers.py

from tests.parallel.test_helpers import (
    double_number,    # x * 2
    square_number,    # x * x
    add_one,          # x + 1
    identity,         # x (unchanged)
    is_even,          # x % 2 == 0
    maybe_raise,      # Raises if x == -1
    slow_square,      # Delays then squares
    MEDIUM_INT_RANGE, # list(range(100))
)

Testing Patterns

Pattern 1: Test Both Thread and Process Paths

from tests.parallel.test_helpers import double_number

def test_both_paths(self):
    """Verify thread and process results match."""
    items = [1, 2, 3, 4, 5]

    # Thread path (lambdas OK)
    thread_result = Parallel.process_in_parallel(
        lambda x: x*2, items, use_processes=False
    )

    # Process path (pickle-safe required)
    process_result = Parallel.process_in_parallel(
        double_number, items, use_processes=True
    )

    # Both should produce same results
    assert thread_result == process_result == [2, 4, 6, 8, 10]

Pattern 2: Error Handling

from tests.parallel.test_helpers import maybe_raise

def test_error_handling(self):
    """Test exception handling with processes."""
    items = [1, -1, 3]  # -1 triggers error

    with pytest.raises(ParallelError) as exc_info:
        Parallel.process_in_parallel(
            maybe_raise,      # ✅ Pickle-safe
            items,
            workers=2,
            use_processes=True
        )

    assert 'Error for value -1' in str(exc_info.value)

Pattern 3: Timeout Testing

from tests.parallel.test_helpers import slow_operation

def test_timeout_handling(self):
    """Test timeout with processes."""
    with pytest.raises(ParallelError):
        Parallel.process_in_parallel(
            slow_operation,   # ✅ Pickle-safe with delay
            [1],
            timeout=0.01,     # Very short timeout
            use_processes=False  # Threads for timeout
        )

Test Files

File	Tests	Focus
test_parallel_thread_vs_process.py	31	Both threads and processes
test_parallel_logic.py	9+	Process-specific tests
test_parallel_logic_comprehensive.py	5+	Process coverage
test_helpers.py	20+ helpers	Pickle-safe functions

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Writing Tests

Basic Structure

"""Tests for module_name - Brief description."""

from unittest.mock import MagicMock, patch

import pytest

from nodupe.module_name import ModuleClass

class TestModuleClass:
    """Test ModuleClass functionality."""

    def test_method_name(self):
        """Test description."""
        # Arrange
        obj = ModuleClass()

        # Act
        result = obj.method()

        # Assert
        assert result == expected

Best Practices

1. Use descriptive test names

   def test_process_in_parallel_with_processes_basic(self):
       """Clear what is being tested."""
   

2. Test both success and error paths

   def test_success_case(self):
       # Test normal operation
   
   def test_error_case(self):
       # Test error handling
   

3. Use fixtures for common setup

   @pytest.fixture
   def sample_data():
       return [1, 2, 3, 4, 5]
   
   def test_with_fixture(self, sample_data):
       # Use sample_data
   

4. Mock external dependencies

   @patch('module.external_service')
   def test_with_mock(self, mock_service):
       # Test with mocked service
   

5. Document thread vs process choice

   # ✅ Pickle-safe - can be used with processes
   double_number
   
   # ❌ Can't pickle - threads only
   lambda x: x * 2
   

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Test Coverage by Module

✅ Complete Modules (95%+ Coverage)

Module	Coverage	Tests
core/api/	100%	400+
database/	98.5%	289
maintenance	99.5%	265
time_sync	92.2%	318
hashing	92.5%	141
scanner_engine	96.5%	226
ml/embedding_cache	99%	57
mime	100%	238
telemetry	100%	16

🟡 Nearly Complete (80-95% Coverage)

Module	Coverage	Tests	Remaining
scanner_engine/processor	88%	32	~12 lines
scanner_engine/walker	86%	21	~14 lines
commands	94%	191	Edge cases
leap_year	60%	45	~100 lines

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Troubleshooting

Common Issues

"Can't pickle local object"

Cause: Using local functions or lambdas with use_processes=True

Solution: Use pickle-safe helpers

# ❌ WRONG
def test_something(self):
    def local_func(x):
        return x * 2
    Parallel.process_in_parallel(local_func, items, use_processes=True)

# ✅ RIGHT
from tests.parallel.test_helpers import double_number
Parallel.process_in_parallel(double_number, items, use_processes=True)

"Test hangs indefinitely"

Cause: Process pool not cleaning up properly

Solution: Add timeout

@pytest.mark.timeout(30)  # 30 second timeout
def test_parallel_operation(self):
    Parallel.process_in_parallel(
        double_number, items, timeout=10.0
    )

"Different results from threads vs processes"

Cause: Race condition or shared state

Solution: Ensure functions are pure (no side effects)

# ❌ WRONG - Has side effects
counter = 0
def increment(x):
    global counter
    counter += 1
    return x + counter

# ✅ RIGHT - Pure function
def double_number(x):
    return x * 2  # No side effects

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Resources

Documentation

• Parallel Testing Guide - Complete guide
• Testing Index - Quick reference
• VerifyTool Completion - Tool implementation

Test Files

• tests/parallel/test_helpers.py - Pickle-safe helpers
• tests/parallel/test_parallel_thread_vs_process.py - Thread vs process tests

Tools

• pytest - Test framework
• coverage.py - Coverage measurement
• pytest-cov - Coverage plugin
• pytest-timeout - Timeout support

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Maintainer: NoDupeLabs Development Team Status: ✅ Complete - All Tests Passing