I'm using Java.
Finally I figured it out: At first I only counted the fewest continous zeros as frequence, and I should also took one into account.

The first time I wrote two decode functions (bits->morse + morse->char), and it got "E" expected "EE"
The second time I simply return morseCode (bits->morse), and it got "." expected "E"

Here is my result:

testBasicBitsDecoding(MorseCodeDecoderTest)

Expected: is "EE"
but: was "E"

With some print I find the input string is "1", why the expected result is "EE" not "E"?

You're absolutely right :D
I wrote this just for convenice and it is somehow a bad habbit keeping using string...

Hi Jolaf,
I printed the decode bits:

testBasicBitsDecoding(MorseCodeDecoderTest)

Expected: is "E"
but: was ".E"

But when I submit it shows:

testBasicBitsDecoding(MorseCodeDecoderTest)

Expected: is "EE"
but: was "E"

I'm confused: why the expected answer is not the same?

Java version:
default function name should be multipleOf3 rather than matchMultipleOf3