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Testing Guide

docs/internal/testing.md

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Testing Guide

This document covers testing practices for Fresh core development.

Test Types

E2E Tests (tests/e2e/)

End-to-end tests simulate real user interactions by sending keyboard/mouse events and examining rendered output. They use the EditorTestHarness which provides a virtual terminal environment.

rust
use crate::common::harness::EditorTestHarness;
use crossterm::event::{KeyCode, KeyModifiers};

#[test]
fn test_basic_editing() {
    let mut harness = EditorTestHarness::new(80, 24).unwrap();

    // Type text
    harness.type_text("Hello").unwrap();

    // Send key combinations
    harness.send_key(KeyCode::Enter, KeyModifiers::NONE).unwrap();

    // Assert on rendered output
    harness.render().unwrap();
    harness.assert_screen_contains("Hello");

    // Assert on buffer content
    harness.assert_buffer_content("Hello\n");
}

Key harness methods:

  • type_text(text) - Type characters
  • send_key(code, modifiers) - Send key events
  • render() - Render to virtual terminal
  • assert_screen_contains(text) - Check rendered output
  • assert_buffer_content(text) - Check buffer content
  • open_file(path) - Open a file
  • with_temp_project(w, h) - Create harness with temp project directory

Shadow Model Validation

For tests focused on text editing operations, enable shadow validation to catch bugs in the piece tree implementation:

rust
#[test]
fn test_editing_operations() {
    let mut harness = EditorTestHarness::new(80, 24).unwrap();
    harness.enable_shadow_validation();  // Enable shadow tracking

    harness.type_text("Hello").unwrap();
    harness.send_key(KeyCode::Backspace, KeyModifiers::NONE).unwrap();

    // assert_buffer_content will also verify shadow model matches
    harness.assert_buffer_content("Hell");
}

The shadow model maintains a simple String that mirrors editing operations. When enabled, assert_buffer_content verifies both the actual buffer and shadow model match.

Property-Based Tests (tests/shadow_model_tests.rs)

The shadow model tests use proptest to generate random sequences of editing operations and verify the TextBuffer (using PieceTree) always matches a simple Vec<u8> oracle:

rust
proptest! {
    #[test]
    fn test_random_edits(ops in vec(edit_operation(), 1..100)) {
        let mut buffer = TextBuffer::new();
        let mut model = Vec::new();

        for op in ops {
            match op {
                Insert(offset, text) => {
                    buffer.insert_bytes(offset, &text);
                    model.splice(offset..offset, text.iter().copied());
                }
                Delete(offset, len) => {
                    buffer.delete_bytes(offset, len);
                    model.drain(offset..offset+len);
                }
            }
            assert_eq!(buffer.to_string(), String::from_utf8_lossy(&model));
        }
    }
}

Test Guidelines

1. No Timeouts

Use semantic waiting instead of fixed timers:

rust
// BAD - flaky
std::thread::sleep(Duration::from_millis(100));

// GOOD - wait for specific state
harness.wait_for_screen_contains("Expected text");

2. Test Isolation

Tests run in parallel. Use isolated resources:

rust
#[test]
fn test_file_operations() {
    // Use temp directories
    let mut harness = EditorTestHarness::with_temp_project(80, 24).unwrap();
    let file_path = harness.project_dir().unwrap().join("test.txt");

    // Internal clipboard mode is enabled by default in harness
}

3. E2E Over Unit Tests

Prefer e2e tests that verify rendered output over unit tests that examine internal state. This catches integration issues and allows refactoring internals freely.

4. Reproduce Before Fixing

Always include a failing test case that reproduces the bug:

rust
#[test]
fn test_issue_123_cursor_bug() {
    let mut harness = EditorTestHarness::new(80, 24).unwrap();
    // Steps that reproduce the bug
    harness.type_text("trigger").unwrap();
    // This assertion should fail without the fix
    harness.assert_cursor_position(0, 7);
}

Running Tests

bash
# Run all tests
cargo test --package fresh-editor

# Run specific e2e test
cargo test --package fresh-editor test_basic_editing

# Run with output
cargo test --package fresh-editor -- --nocapture

# Run property tests with more cases
PROPTEST_CASES=1000 cargo test shadow_model

Test Organization

tests/
├── common/
│   ├── harness.rs       # EditorTestHarness
│   └── fixtures.rs      # Test file helpers
├── e2e/                 # End-to-end tests
│   ├── basic.rs
│   ├── encoding.rs
│   └── ...
├── shadow_model_tests.rs    # Property-based buffer tests
├── property_tests.rs        # Other property tests
└── integration_tests.rs     # Integration tests