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Came up with a useful #Rails pattern – combining `uniq` and `sole` to get a value if unique, and raise otherwise.
```
DEV (main)> [ 1, 1, 1 ].uniq.sole
1
DEV (main)> [ 1, 1, 2 ].uniq.sole
(irb):135:in `<main>': multiple items found (Enumerable::SoleItemExpectedError)
```
Using it in a spec to get a single class from multiple records assumed to have the same class:
```
transaction_class = [ transaction_1, transaction_2 ].map(&:class).uniq.sole
expect(transaction_class.some_scope).to …
```
@henrik this is great! 
@henrik also, crashing in tests is so underrated. I've often seen checks like this expressed as
assert_equal 1, [1,1,1].uniq.lenght
Most often something like
assert_equal 1, results.length
assert_equal "foo", results.first
@mark Yeah, crashing is great. You can often get clearer info sooner. Using `Item.last!` instead of `Item.last` and so on (getting an exception instead of nil) is one I use a lot. There’s rarely good reason not to use that one if you expect a value (in tests or otherwise).