Good implementation of unit test with EasyMock

I have a question about good implementation of unit test with EasyMock.

First implementation:

Capture<String> capturedString = newCapture();
myService.doSomething(capture(capturedString));
expectLastCall();

assertEquals("stringValue", catpuredString.getValue());

Second implementation:

myService.doSomething("stringValue");
expectLastCall();

I feel comfortable with the first implementation because an assertion is present. But in the second implementation I expect "stringValue" passed to my service. If it's not the case an exception will be thrown by EasyMock. So is there a difference between the 2 implementations ? If not, is one better then the other ?

Thanks.