Hi,
The junitlauncher does not identify and execute unit test which uses mocking framework Mockito. The other unit test cases which are not using the mocking framework are identified and executed successfully. Also, the IntelliJ Idea IDE successfully executes the unit test which uses mocking framework Mockito.

Execution Log:
 [junitlauncher] Test run finished after 0 ms
 [junitlauncher] [         1 containers found      ]
 [junitlauncher] [         0 containers skipped    ]
 [junitlauncher] [         1 containers started    ]
 [junitlauncher] [         0 containers aborted    ]
 [junitlauncher] [         1 containers successful ]
 [junitlauncher] [         0 containers failed     ]
 [junitlauncher] [         0 tests found           ]
 [junitlauncher] [         0 tests skipped         ]
 [junitlauncher] [         0 tests started         ]
 [junitlauncher] [         0 tests aborted         ]
 [junitlauncher] [         0 tests successful      ]
 [junitlauncher] [         0 tests failed          ]

Environment:
OS: Winodws 10 and Centos 7
IDE: IntelliJ Idea 2019.1.3, 2020.1
ANT: 1.10.5
Mockito: 3.3.3
JDK: OpenJDK 1.8 

Code:
@ExtendWith(MockitoExtension.class)
class FileHandlerTest {

    @Mock
    ServletContext application;

    @Test
    void getLegacyStaticFilePath() {
        FileHandler underTest = new FileHandler();
        when(application.getAttribute("envglobal")).thenReturn("windev");

        Map<String, String> filePathMap=underTest.getLegacyStaticFilePath("csv",application);

        assertAll("static file path",
                () -> assertEquals("C:\\gta\\supportive_documents\\", filePathMap.get("supportDoc")),
                () -> assertEquals("C:\\gta\\gtc_load\\", filePathMap.get("loadDoc")),
                () -> assertEquals("C:\\gta\\ttg_reports\\", filePathMap.get("ttgReportsDoc")));
    }
}

Other Observation:
Test report TEST-com.XXX.FileHandlerTest.txt created with 0 byte.