Assertions are inconsistent with and more limited than bats-assert

[inkarkat]

I've started using bats-assert and am now looking into how bats-file can help with file-based assertions. As both libraries are built on bats-support (and have originated from the same author), I see these as closely related projects, and expect consistency in their APIs. However, there seem to be differences that make adoption harder:

• bats-assert uses assert and refute to distinguish between positive and negative assertions, whereas bats-file uses assert_something and assert_not_something. For example, assert_file_not_exists should be named refute_file_exists to be consistent with bats-assert.
• Some negative assertions are missing, e.g. there's no assert_file_size_not_equals (or rather refute_file_size_equals), and no refute_files_equal.
• assert_file_contains only does regexp matching; the related assert_output from bats-assert offers complete equivalence, partial (but literal) matching, and regexp matching, making it far more versatile.

All of bats-file's assertions are thin wrappers around test commands; its main value is in providing a fluent, consistent, and discoverable API. I suggest to align the API with bats-assert, and to add the missing negative assertions and more matching options to assert_file_contains. This would make the library more powerful and easier to use for users already familiar with bats-assert.