Add tests

Added tests.

One is to test `convert_rate` and `reverse_converse_rate` in `download_manager.py`.

src/tribler/core/components/libtorrent/download_manager/download_manager.py

@@ -140,10 +140,9 @@ def convert_rate(rate: int) -> int:
         """
         if rate == 0:
             return -1
-        elif rate == -1:
+        if rate == -1:
             return 1
-        else:
-            return rate * 1024
+        return rate * 1024
 
     @staticmethod
     def reverse_convert_rate(rate: int) -> int:
@@ -153,10 +152,9 @@ def reverse_convert_rate(rate: int) -> int:
         """
         if rate == -1:
             return 0
-        elif rate == 1:
+        if rate == 1:
             return -1
-        else:
-            return rate // 1024
+        return rate // 1024
 
     async def _check_dht_ready(self, min_dht_peers=60):
         """

src/tribler/core/components/libtorrent/tests/test_download_manager.py

@@ -274,6 +274,20 @@ async def test_start_download_existing_handle(fake_dlmgr):
     await download.shutdown()
 
 
+def test_convert_rate():
+    assert DownloadManager.convert_rate(0) == -1  # 0 is a special value
+    assert DownloadManager.convert_rate(-1) == 1  # -1 is a special value
+    for test_num in [1, 2, -2]:
+        assert DownloadManager.convert_rate(test_num) == test_num * 1024
+
+
+def test_reverse_convert_rate():
+    assert DownloadManager.reverse_convert_rate(-1) == 0  # -1 is a special value
+    assert DownloadManager.reverse_convert_rate(1) == -1  # 1 is a special value
+    for test_num in [0, 2, -2]:
+        assert DownloadManager.reverse_convert_rate(test_num) == test_num // 1024
+
+
 def test_start_download_existing_download(fake_dlmgr):
     """
     Testing the addition of a torrent to the libtorrent manager, if there is a pre-existing download.