"Take 2 strings s1 and s2 including only letters from a to z."

"Take 2 strings s1 and s2 including only letters from a to z." It's defined in the instructions, so the tests are complete.

"but still this solution seems to be correct, because task guarantees that only letters will be passed in. solution does not have to check for non-letters."

That is fair I suppose.

• solution has to be correct to be posted here.
• any solution is just as correct as far the tests go. If tests are poor, invalid solutions can slip through.
• but still this solution seems to be correct, because task guarantees that only letters will be passed in. solution does not have to check for non-letters.

I thought a solution had to be correct to be posted here?

This is incorrect. It does not test for non-leters.

As others have pointed out, the assertions are broken. You can either fix it by running abs/1 on the difference between expected and actual, or, better yet, ditch your home made assertion and use ExUnit's assert_in_delta.

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Ruby methods are idiomatically snake case. Rename method str_count.

This issue hasn't been resolved. The Elixir version should be bumped to something 1.4.x, and the tests should all expect strings. Can we ping @jhoffner, who is sensei for the kata? How do I get involved fixing it?

Ruby version of Create Phone Number is not idiomatic. Method names should be underscored, not camelCased.