Unit Testing Android Studio
Some notes:


This is not a unit test of your code. A unit test must at some point involve some part of your code, and it looks like this test uses only classes which exist in the Java SDK. The idea is not to check an idea for an implementation, but instead to detect bugs in your actual implementation.
By convention instance variables use camelCase in Java, so ExpectedResult should be expectedResult and str_time2 should be strTime2.
Maybe it's necessary, but I'm sceptical of the need for the conversion from Date to DateTime.