test: Add pytest infrastructure and attachment tests

In making my last fix to attachments, I found it challenging not
having tests to ensure there was no regression.

Added pytest with minimal setup and isolated configuration. Created
a separate test workflow to keep tests isolated from linting.

Tests cover the key elements of the attachment logic:
- URL extraction from issue bodies
- Filename extraction from different URL types
- Filename collision resolution
- Manifest duplicate prevention

.github/workflows/test.yml

@@ -0,0 +1,33 @@
+---
+name: "test"
+
+# yamllint disable-line rule:truthy
+on:
+  pull_request:
+    branches:
+      - "*"
+  push:
+    branches:
+      - "main"
+      - "master"
+
+jobs:
+  test:
+    name: test
+    runs-on: ubuntu-24.04
+    strategy:
+      matrix:
+        python-version: ["3.10", "3.11", "3.12", "3.13", "3.14"]
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v5
+        with:
+          fetch-depth: 0
+      - name: Setup Python
+        uses: actions/setup-python@v6
+        with:
+          python-version: ${{ matrix.python-version }}
+          cache: "pip"
+      - run: pip install -r release-requirements.txt
+      - run: pytest tests/ -v

pytest.ini

@@ -0,0 +1,6 @@
+[pytest]
+testpaths = tests
+python_files = test_*.py
+python_classes = Test*
+python_functions = test_*
+addopts = -v

release-requirements.txt

@@ -8,6 +8,7 @@ colorama==0.4.6
 docutils==0.22.3
 flake8==7.3.0
 gitchangelog==3.0.4
+pytest==8.3.3
 idna==3.11
 importlib-metadata==8.7.0
 jaraco.classes==3.4.0

tests/__init__.py

@@ -0,0 +1 @@
+"""Tests for python-github-backup."""

tests/test_attachments.py

@@ -0,0 +1,353 @@
+"""Behavioral tests for attachment functionality."""
+
+import json
+import os
+import tempfile
+from pathlib import Path
+from unittest.mock import Mock
+
+import pytest
+
+from github_backup import github_backup
+
+
+@pytest.fixture
+def attachment_test_setup(tmp_path):
+    """Fixture providing setup and helper for attachment download tests."""
+    from unittest.mock import patch
+
+    issue_cwd = tmp_path / "issues"
+    issue_cwd.mkdir()
+
+    # Mock args
+    args = Mock()
+    args.as_app = False
+    args.token_fine = None
+    args.token_classic = None
+    args.username = None
+    args.password = None
+    args.osx_keychain_item_name = None
+    args.osx_keychain_item_account = None
+    args.user = "testuser"
+    args.repository = "testrepo"
+
+    repository = {"full_name": "testuser/testrepo"}
+
+    def call_download(issue_data, issue_number=123):
+        """Call download_attachments with mocked HTTP downloads.
+
+        Returns list of URLs that were actually downloaded.
+        """
+        downloaded_urls = []
+
+        def mock_download(url, path, auth, as_app, fine):
+            downloaded_urls.append(url)
+            return {
+                "success": True,
+                "saved_as": os.path.basename(path),
+                "url": url,
+            }
+
+        with patch(
+            "github_backup.github_backup.download_attachment_file",
+            side_effect=mock_download,
+        ):
+            github_backup.download_attachments(
+                args, str(issue_cwd), issue_data, issue_number, repository
+            )
+
+        return downloaded_urls
+
+    return {
+        "issue_cwd": str(issue_cwd),
+        "args": args,
+        "repository": repository,
+        "call_download": call_download,
+    }
+
+
+class TestURLExtraction:
+    """Test URL extraction with realistic issue content."""
+
+    def test_mixed_urls(self):
+        issue_data = {
+            "body": """
+            ## Bug Report
+
+            When uploading files, I see this error. Here's a screenshot:
+            https://github.com/user-attachments/assets/abc123def456
+
+            The logs show: https://github.com/user-attachments/files/789/error-log.txt
+
+            This is similar to https://github.com/someorg/somerepo/issues/42 but different.
+
+            You can also see the video at https://user-images.githubusercontent.com/12345/video-demo.mov
+
+            Here's how to reproduce:
+            ```bash
+            # Don't extract this example URL:
+            curl https://github.com/user-attachments/assets/example999
+            ```
+
+            More info at https://docs.example.com/guide
+
+            Also see this inline code `https://github.com/user-attachments/files/111/inline.pdf` should not extract.
+
+            Final attachment: https://github.com/user-attachments/files/222/report.pdf.
+            """,
+            "comment_data": [
+                {
+                    "body": "Here's another attachment: https://private-user-images.githubusercontent.com/98765/secret.png?jwt=token123"
+                },
+                {
+                    "body": """
+                    Example code:
+                    ```python
+                    url = "https://github.com/user-attachments/assets/code-example"
+                    ```
+                    But this is real: https://github.com/user-attachments/files/333/actual.zip
+                    """
+                },
+            ],
+        }
+
+        # Extract URLs
+        urls = github_backup.extract_attachment_urls(issue_data)
+
+        expected_urls = [
+            "https://github.com/user-attachments/assets/abc123def456",
+            "https://github.com/user-attachments/files/789/error-log.txt",
+            "https://user-images.githubusercontent.com/12345/video-demo.mov",
+            "https://github.com/user-attachments/files/222/report.pdf",
+            "https://private-user-images.githubusercontent.com/98765/secret.png?jwt=token123",
+            "https://github.com/user-attachments/files/333/actual.zip",
+        ]
+
+        assert set(urls) == set(expected_urls)
+
+    def test_trailing_punctuation_stripped(self):
+        """URLs with trailing punctuation should have punctuation stripped."""
+        issue_data = {
+            "body": """
+            See this file: https://github.com/user-attachments/files/1/doc.pdf.
+            And this one (https://github.com/user-attachments/files/2/image.png).
+            Check it out! https://github.com/user-attachments/files/3/data.csv!
+            """
+        }
+
+        urls = github_backup.extract_attachment_urls(issue_data)
+
+        expected = [
+            "https://github.com/user-attachments/files/1/doc.pdf",
+            "https://github.com/user-attachments/files/2/image.png",
+            "https://github.com/user-attachments/files/3/data.csv",
+        ]
+        assert set(urls) == set(expected)
+
+    def test_deduplication_across_body_and_comments(self):
+        """Same URL in body and comments should only appear once."""
+        duplicate_url = "https://github.com/user-attachments/assets/abc123"
+
+        issue_data = {
+            "body": f"First mention: {duplicate_url}",
+            "comment_data": [
+                {"body": f"Second mention: {duplicate_url}"},
+                {"body": f"Third mention: {duplicate_url}"},
+            ],
+        }
+
+        urls = github_backup.extract_attachment_urls(issue_data)
+
+        assert set(urls) == {duplicate_url}
+
+
+class TestFilenameExtraction:
+    """Test filename extraction from different URL types."""
+
+    def test_modern_assets_url(self):
+        """Modern assets URL returns UUID."""
+        url = "https://github.com/user-attachments/assets/abc123def456"
+        filename = github_backup.get_attachment_filename(url)
+        assert filename == "abc123def456"
+
+    def test_modern_files_url(self):
+        """Modern files URL returns filename."""
+        url = "https://github.com/user-attachments/files/12345/report.pdf"
+        filename = github_backup.get_attachment_filename(url)
+        assert filename == "report.pdf"
+
+    def test_legacy_cdn_url(self):
+        """Legacy CDN URL returns filename with extension."""
+        url = "https://user-images.githubusercontent.com/123456/abc-def.png"
+        filename = github_backup.get_attachment_filename(url)
+        assert filename == "abc-def.png"
+
+    def test_private_cdn_url(self):
+        """Private CDN URL returns filename."""
+        url = "https://private-user-images.githubusercontent.com/98765/secret.png?jwt=token123"
+        filename = github_backup.get_attachment_filename(url)
+        assert filename == "secret.png"
+
+    def test_repo_files_url(self):
+        """Repo-scoped files URL returns filename."""
+        url = "https://github.com/owner/repo/files/789/document.txt"
+        filename = github_backup.get_attachment_filename(url)
+        assert filename == "document.txt"
+
+
+class TestFilenameCollision:
+    """Test filename collision resolution."""
+
+    def test_collision_behavior(self):
+        """Test filename collision resolution with real files."""
+        with tempfile.TemporaryDirectory() as tmpdir:
+            # No collision - file doesn't exist
+            result = github_backup.resolve_filename_collision(
+                os.path.join(tmpdir, "report.pdf")
+            )
+            assert result == os.path.join(tmpdir, "report.pdf")
+
+            # Create the file, now collision exists
+            Path(os.path.join(tmpdir, "report.pdf")).touch()
+            result = github_backup.resolve_filename_collision(
+                os.path.join(tmpdir, "report.pdf")
+            )
+            assert result == os.path.join(tmpdir, "report_1.pdf")
+
+            # Create report_1.pdf too
+            Path(os.path.join(tmpdir, "report_1.pdf")).touch()
+            result = github_backup.resolve_filename_collision(
+                os.path.join(tmpdir, "report.pdf")
+            )
+            assert result == os.path.join(tmpdir, "report_2.pdf")
+
+    def test_manifest_reserved(self):
+        """manifest.json is always treated as reserved."""
+        with tempfile.TemporaryDirectory() as tmpdir:
+            # Even if manifest.json doesn't exist, should get manifest_1.json
+            result = github_backup.resolve_filename_collision(
+                os.path.join(tmpdir, "manifest.json")
+            )
+            assert result == os.path.join(tmpdir, "manifest_1.json")
+
+
+class TestManifestDuplicatePrevention:
+    """Test that manifest prevents duplicate downloads (the bug fix)."""
+
+    def test_manifest_filters_existing_urls(self, attachment_test_setup):
+        """URLs in manifest are not re-downloaded."""
+        setup = attachment_test_setup
+
+        # Create manifest with existing URLs
+        attachments_dir = os.path.join(setup["issue_cwd"], "attachments", "123")
+        os.makedirs(attachments_dir)
+        manifest_path = os.path.join(attachments_dir, "manifest.json")
+
+        manifest = {
+            "attachments": [
+                {
+                    "url": "https://github.com/user-attachments/assets/old1",
+                    "success": True,
+                    "saved_as": "old1.pdf",
+                },
+                {
+                    "url": "https://github.com/user-attachments/assets/old2",
+                    "success": True,
+                    "saved_as": "old2.pdf",
+                },
+            ]
+        }
+        with open(manifest_path, "w") as f:
+            json.dump(manifest, f)
+
+        # Issue data with 2 old URLs and 1 new URL
+        issue_data = {
+            "body": """
+            Old: https://github.com/user-attachments/assets/old1
+            Old: https://github.com/user-attachments/assets/old2
+            New: https://github.com/user-attachments/assets/new1
+            """
+        }
+
+        downloaded_urls = setup["call_download"](issue_data)
+
+        # Should only download the NEW URL (old ones filtered by manifest)
+        assert len(downloaded_urls) == 1
+        assert downloaded_urls[0] == "https://github.com/user-attachments/assets/new1"
+
+    def test_no_manifest_downloads_all(self, attachment_test_setup):
+        """Without manifest, all URLs should be downloaded."""
+        setup = attachment_test_setup
+
+        # Issue data with 2 URLs
+        issue_data = {
+            "body": """
+            https://github.com/user-attachments/assets/url1
+            https://github.com/user-attachments/assets/url2
+            """
+        }
+
+        downloaded_urls = setup["call_download"](issue_data)
+
+        # Should download ALL URLs (no manifest to filter)
+        assert len(downloaded_urls) == 2
+        assert set(downloaded_urls) == {
+            "https://github.com/user-attachments/assets/url1",
+            "https://github.com/user-attachments/assets/url2",
+        }
+
+    def test_manifest_skips_permanent_failures(self, attachment_test_setup):
+        """Manifest skips permanent failures (404, 410) but retries transient (503)."""
+        setup = attachment_test_setup
+
+        # Create manifest with different failure types
+        attachments_dir = os.path.join(setup["issue_cwd"], "attachments", "123")
+        os.makedirs(attachments_dir)
+        manifest_path = os.path.join(attachments_dir, "manifest.json")
+
+        manifest = {
+            "attachments": [
+                {
+                    "url": "https://github.com/user-attachments/assets/success",
+                    "success": True,
+                    "saved_as": "success.pdf",
+                },
+                {
+                    "url": "https://github.com/user-attachments/assets/notfound",
+                    "success": False,
+                    "http_status": 404,
+                },
+                {
+                    "url": "https://github.com/user-attachments/assets/gone",
+                    "success": False,
+                    "http_status": 410,
+                },
+                {
+                    "url": "https://github.com/user-attachments/assets/unavailable",
+                    "success": False,
+                    "http_status": 503,
+                },
+            ]
+        }
+        with open(manifest_path, "w") as f:
+            json.dump(manifest, f)
+
+        # Issue data has all 4 URLs
+        issue_data = {
+            "body": """
+            https://github.com/user-attachments/assets/success
+            https://github.com/user-attachments/assets/notfound
+            https://github.com/user-attachments/assets/gone
+            https://github.com/user-attachments/assets/unavailable
+            """
+        }
+
+        downloaded_urls = setup["call_download"](issue_data)
+
+        # Should only retry 503 (transient failure)
+        # Success, 404, and 410 should be skipped
+        assert len(downloaded_urls) == 1
+        assert (
+            downloaded_urls[0]
+            == "https://github.com/user-attachments/assets/unavailable"
+        )