Test for binary file diff passed when it should not have

[dandavison]

Why did the test in #94 pass at af84d5c when it should not have?

[wescande]

The test pass because the source is Unknown, so the output is replicated direclty

The test would have failed if there was no newline here

something like this:

   const BINARY_FILES_DIFFER: &str = "commit ad023698217b086f1bef934be62b4523c95f64d9 (HEAD -> master)
Author: Dan Davison <[email protected]>
Date:   Wed Feb 12 08:05:53 2020 -0600
    .
diff --git a/foo b/foo
new file mode 100644
index 0000000..b572921
Binary files /dev/null and b/foo differ
";