New cop: Minitest/AssertSame

[fatkodima]

https://docs.ruby-lang.org/en/2.1.0/MiniTest/Assertions.html#method-i-assert_same

# bad
assert foo.equal?(bar)
refute foo.equal?(bar)

# good
assert_same foo, bar
refute_same foo, bar

In the rails/rails codebase by a quick regexp search I found 30+ offenses of this.

[koic]

Good catch! This will open a PR in the style guide first.

[andyw8]

I have a slight concern here: same is less explicit than equal?. It's not obvious what kind of comparison is being made (==, eql?, etc. ) unless you look at the implementation or docs.