Ruby跑test assert_equal出来的结果分明是一样的为什么还是失败？

看Ruby第二天Orz....
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Run options:

# Running tests:

.F

Finished tests in 0.002672s, 748.3980 tests/s, 748.3980 assertions/s.

1) Failure:
test_two(HuamiTest) [/home/meck/Playground/huami.rb/test/test_huami.rb:11]:
<"K924748b267770BE"> expected but was
<"k924748b267770BE">.

2 tests, 2 assertions, 1 failures, 0 errors, 0 skips
rake aborted!
Command failed with status (1): [/usr/bin/ruby -I"lib:test" -I"/usr/lib/rub...]