* Keep commits discrete. Avoid including multiple unrelated changes in a single commit.
* Keep commits self-contained. Avoid spreading a single change across multiple commits. A single commit should make sense in isolation.

### Testing changes

    changes to lower the maintenance cost.
*   Bug fixes also generally require unit tests, because the presence of bugs
    usually indicates insufficient test coverage.
*   Keep API compatibility in mind when you change code in core TensorFlow,
    e.g., code in
    [tensorflow/core](https://github.com/tensorflow/tensorflow/tree/master/tensorflow/core)
    and