This PR adds three tests relating to the mask node, which makes a new mask data block for `node_mask`, creates an invalid input test, and covers the `fixed/scene` case. Coverage: - Function: 88.89% -> 88.89% - Line: 91.41% -> 94.53% - Region: 83.33% -> 88.10% - Branch: 62.50% -> 81.25% Pull Request: https://projects.blender.org/blender/blender/pulls/142447