Improve test suite: remove mocks and add 0.8.x migration tests

- Remove mock-based tests from plugin tests (headers, singlefile, ublock, captcha2)
- Replace fake cache tests with real double-install tests that verify cache behavior
- Add SCHEMA_0_8 and seed_0_8_data() for testing 0.8.x data directory migrations
- Add TestMigrationFrom08x class with comprehensive migration tests:
  - Snapshot count preservation
  - Crawl record preservation
  - Snapshot-to-crawl relationship preservation
  - Tag preservation
  - ArchiveResult status preservation
  - CLI command verification after migration
- Add more CLI tests for add command (tags, multiple URLs, file input)
- All tests now use real functionality without mocking

tests/test_add.py

@@ -74,3 +74,96 @@ def test_add_creates_crawl_in_database(tmp_path, process, disable_extractors_dic
     conn.close()
 
     assert count >= 1
+
+
+def test_add_with_tags(tmp_path, process, disable_extractors_dict):
+    """Test adding URL with tags."""
+    os.chdir(tmp_path)
+    subprocess.run(
+        ["archivebox", "add", "--index-only", "--depth=0", "--tag=test,example", "https://example.com"],
+        capture_output=True,
+        env=disable_extractors_dict,
+    )
+
+    # Check that tags were created in database
+    conn = sqlite3.connect("index.sqlite3")
+    c = conn.cursor()
+    tags = c.execute("SELECT name FROM core_tag").fetchall()
+    conn.close()
+
+    tag_names = [t[0] for t in tags]
+    assert 'test' in tag_names or 'example' in tag_names
+
+
+def test_add_multiple_urls_single_call(tmp_path, process, disable_extractors_dict):
+    """Test adding multiple URLs in a single call creates multiple snapshots."""
+    os.chdir(tmp_path)
+    subprocess.run(
+        ["archivebox", "add", "--index-only", "--depth=0",
+         "https://example.com", "https://example.org"],
+        capture_output=True,
+        env=disable_extractors_dict,
+    )
+
+    # Check both URLs are in the source file
+    sources_dir = tmp_path / "sources"
+    source_files = list(sources_dir.glob("*cli_add.txt"))
+    assert len(source_files) >= 1
+    source_content = source_files[0].read_text()
+    assert "example.com" in source_content
+    assert "example.org" in source_content
+
+
+def test_add_from_file(tmp_path, process, disable_extractors_dict):
+    """Test adding URLs from a file."""
+    os.chdir(tmp_path)
+
+    # Create a file with URLs
+    urls_file = tmp_path / "urls.txt"
+    urls_file.write_text("https://example.com\nhttps://example.org\n")
+
+    subprocess.run(
+        ["archivebox", "add", "--index-only", "--depth=0", str(urls_file)],
+        capture_output=True,
+        env=disable_extractors_dict,
+    )
+
+    # Check that a Crawl was created
+    conn = sqlite3.connect("index.sqlite3")
+    c = conn.cursor()
+    count = c.execute("SELECT COUNT(*) FROM crawls_crawl").fetchone()[0]
+    conn.close()
+
+    assert count >= 1
+
+
+class TestAddCLI:
+    """Test the CLI interface for add command."""
+
+    def test_add_help(self, tmp_path, process):
+        """Test that --help works for add command."""
+        os.chdir(tmp_path)
+
+        result = subprocess.run(
+            ["archivebox", "add", "--help"],
+            capture_output=True,
+            text=True,
+        )
+
+        assert result.returncode == 0
+        assert '--depth' in result.stdout or 'depth' in result.stdout
+        assert '--tag' in result.stdout or 'tag' in result.stdout
+
+    def test_add_no_args_shows_help(self, tmp_path, process):
+        """Test that add with no args shows help or usage."""
+        os.chdir(tmp_path)
+
+        result = subprocess.run(
+            ["archivebox", "add"],
+            capture_output=True,
+            text=True,
+        )
+
+        # Should either show help or error about missing URL
+        combined = result.stdout + result.stderr
+        assert 'usage' in combined.lower() or 'url' in combined.lower() or 'add' in combined.lower()