BUG: reset setitem_copy on object enlargement
TST: eliminate SettingWithCopyWarnings in tests (catch them)

TST: tests for GH5597

BUG: don't set copy on equal indexes after an operation
TST: add testing base TestCase to provide global testing config
TST: changed refs to use testing/TestCase where setUpClass/tearDownClass are defined
TST: change from using unittest.TestCase directly to using pandas.util.testing.TestCase