diff --git a/docs/test-matrix.md b/docs/test-matrix.md
index 6115407..53dc7a2 100644
--- a/docs/test-matrix.md
+++ b/docs/test-matrix.md
@@ -8,11 +8,14 @@ Use the smallest relevant check while iterating:
 | Check for compile errors quickly | `cargo check` | Any supported Rust platform |
 | Run lints across binaries and tests | `cargo clippy --all-targets` | Any supported Rust platform with `clippy` |
 | Validate CPU reference operations | `cargo test --lib --bins` | Any supported Rust platform |
+| Test asset downloads without network access | `python3 -m unittest discover -s python -p 'test_*.py'` | Python 3; standard library only |
 | Check Metal-to-CPU kernel parity | `cargo test --test parity -- --nocapture` | Apple Silicon macOS |
 | Check end-to-end GPT-2 predictions | `cargo test --test gpt2_e2e -- --nocapture` | Requires downloaded GPT-2 assets |
 
 Run these commands from the repository root. For a lightweight CPU-only preflight, run `cargo fmt --check`, `cargo check`, and `cargo test --lib --bins`; add `cargo clippy --all-targets` when the Clippy component is installed.
 
+Downloader regressions use mocked HTTP responses to check completed, failed, empty, and truncated transfers, timeout validation, and forced refresh. They do not download pretrained model files or require the Python ML dependencies.
+
 Before the end-to-end check, download the model weights and tokenizer:
 
 ```bash