Add some checks to catch test failure

Really just checking that the setup is able to create test files so it
is known they were there then removed.
Windows tests really need verification of
recycle, which is not present.

tests/test_plat_other.py

@@ -32,6 +32,7 @@ def testfile():
         dir=op.expanduser("~"), prefix="send2trash_test", delete=False
     )
     file.close()
+    assert op.exists(file) is True
     yield file
     # Cleanup trash files on supported platforms
     if sys.platform != "win32":
@@ -57,6 +58,7 @@ def testfiles():
         )
     )
     [file.close() for file in files]
+    assert all([op.exists(file) for file in files]) is True
     yield files
     filenames = [op.basename(file.name) for file in files]
     [os.remove(op.join(HOMETRASH, "files", filename)) for filename in filenames]
@@ -93,6 +95,7 @@ def testUnicodefile():
     name = u"send2trash_tést1"
     file = op.join(op.expanduser(b"~"), name.encode("utf-8"))
     touch(file)
+    assert op.exists(file) is True
     yield file
     # Cleanup trash files on supported platforms
     if sys.platform != "win32":
@@ -158,6 +161,7 @@ def testExtVol():
     fileName = "test.txt"
     filePath = op.join(volume.trashTopdir, fileName)
     touch(filePath)
+    assert op.exists(filePath) is True
     yield volume, fileName, filePath
     volume.cleanup()