Testing the input to jmeter, the correct way to pass the parameter through text or csv file, follow these steps as,
1. Create a text file (or csv file) containing usernames and passwords separated by commas. Put this in the same directory as your test plan, as

2. Add the CSV DataSet configuration item to the test plan. Name the variables USER and PASS. Also, add the path to the file name in this element (I have sure to check the path to the file) as

3. Fill in the username with $ {USER} and password with $ {PASS} in the login sampler (HTTP Request) as, 
Hope this helps you
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