junit as external jar or library

what is difference bewteen adding junit as external jar or as Libray as attached.

I got error initally saying Error: Could not find or load main class
when i run as juni tclass.

when i added Library then junit 4(earlier it was only added as external jar) i was able to run the test case.

Please advise.
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when i run as juni tclass.
Are you saying that you're trying to run JUnit as an app? If so, that's not what you're meant to do
gudii9Author Commented:
In eclipse i was right clicking on the junit class say xyzrtest.java then run as JUnit TEst class then getting error
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gudii9Author Commented:
run time errOR I am getting is
Error: Could not find or load main class
when i run as junit class by right clicking on that junit class in eclipse.
sounds like the app doesn't have the main class set in its configuration in eclipse

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gudii9Author Commented:
as it is junit no need of junit right. but it got resolved when i added JUnit Library later(initially i added junit as external library as in screenshot in original question which did not resolve the issue though). my question is difference between adding as Library and adding as external jar?
gudii9Author Commented:
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