Add GdUnit4 testing framework with comprehensive test coverage

- Add GdUnit4 v6.2.1 framework in addons/gdUnit4/
- Create test directory structure (tests/unit/, tests/integration/, tests/mocks/)
- Add unit tests for MusicPlayer.gd (8 tests)
- Add unit tests for MainWindow.gd (15+ tests)
- Add unit tests for Settings.gd (5 tests)
- Add unit tests for Playlist.gd (11 tests)
- Add integration tests for full flow (10+ tests)
- Add MockHTTPRequest for HTTP request mocking
- Add TestHelpers with utility functions
- Add Gitea Actions CI workflow (.gitea/workflows/test.yml)
- Add .runsettings for GdUnit4 CLI configuration
- Add run_tests.sh for convenient test execution
- Add TESTING.md with comprehensive documentation
- Add TESTING_PLAN.md with implementation details
- Update .gitignore for test artifacts
- Enable GdUnit4 plugin in project.godot

Features:
- Test button functionality (play, pause, search, sync, etc.)
- Mock REST API requests to server
- Test complete application flows
- Run tests in CI (headless mode)
- Run tests in GUI for visual feedback
- JUnit XML and HTML test reports

Generated by OpenCode AI assistant.

run_tests.sh

@@ -0,0 +1,82 @@
+#!/bin/bash
+
+# GdUnit4 Test Runner for MusicPlayer
+# Usage: ./run_tests.sh [--headless] [--verbose]
+
+set -e
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+cd "$SCRIPT_DIR"
+
+# Default flags
+HEADLESS=false
+VERBOSE=false
+
+# Parse arguments
+for arg in "$@"; do
+    case "$arg" in
+        --headless)
+            HEADLESS=true
+            ;;
+        --verbose)
+            VERBOSE=true
+            ;;
+    esac
+done
+
+# Godot executable (adjust if needed)
+GODOT_EXEC="godot"
+
+# Check if Godot is available
+if ! command -v "$GODOT_EXEC" &> /dev/null; then
+    echo "Error: Godot executable not found at: $GODOT_EXEC"
+    echo "Please ensure Godot 4.7 is installed and in your PATH"
+    exit 1
+fi
+
+# Build arguments
+GODOT_ARGS=(
+    "--path" "."
+    "-s" "addons/gdUnit4/test.gd"
+    "--gdunit.cli"
+)
+
+if [ "$HEADLESS" = true ]; then
+    GODOT_ARGS+=("--headless")
+fi
+
+if [ "$VERBOSE" = true ]; then
+    GODOT_ARGS+=("--verbose")
+fi
+
+echo "Running tests with Godot..."
+echo "Command: $GODOT_EXEC ${GODOT_ARGS[*]}"
+echo ""
+
+# Run tests
+"$GODOT_EXEC" "${GODOT_ARGS[@]}"
+EXIT_CODE=$?
+
+# Check results
+echo ""
+if [ $EXIT_CODE -eq 0 ]; then
+    echo "✓ All tests passed!"
+else
+    echo "✗ Tests failed with exit code: $EXIT_CODE"
+fi
+
+# Check for test results files
+if [ -f "test_results.xml" ]; then
+    echo ""
+    echo "Test results:"
+    echo "  - JUnit XML: test_results.xml"
+    echo "  - HTML: test_results.html"
+    
+    # Count failures
+    FAILURES=$(grep -c '<failure' test_results.xml || true)
+    if [ "$FAILURES" -gt 0 ]; then
+        echo "  - Failures: $FAILURES"
+    fi
+fi
+
+exit $EXIT_CODE