PackageType mockPackageType = mock(PackageType.class);
when(objectUnderTest.discoverDeployedPackages(any(PackageType.class))).thenCallRealMethod();
//run code under test
Set<ResourcePackageDetails> actualResult = objectUnderTest.discoverDeployedPackages(mockPackageType);
//verify the results (Assert and mock verification)
Assert.assertEquals(actualResult.size(), 0);
verify(mockResourceContext, times(1)).getPluginConfiguration();