Update unit tests for testing linux behavior

src/tests/test_torrent.py

@@ -45,7 +45,6 @@ def test_ensure_aria2c_returns_windows_path(monkeypatch):
 
     assert torrent.ensure_aria2c() == expected
 
-
 def test_ensure_aria2c_installs_when_not_found(monkeypatch):
     monkeypatch.setattr(
         torrent,
@@ -53,6 +52,12 @@ def test_ensure_aria2c_installs_when_not_found(monkeypatch):
         Mock(return_value=None),
     )
 
+    monkeypatch.setattr(
+        torrent.sys,
+        "platform",
+        "win32",
+    )
+
     installer = Mock(
         return_value="/fake/aria2c.exe"
     )
@@ -73,6 +78,60 @@ def test_ensure_aria2c_installs_when_not_found(monkeypatch):
         log_fn=torrent.log,
     )
 
+def test_ensure_aria2c_linux_returns_installed_binary(monkeypatch):
+    monkeypatch.setattr(
+        torrent.sys,
+        "platform",
+        "linux",
+    )
+
+    monkeypatch.setattr(
+        torrent,
+        "find_aria2c",
+        Mock(return_value="/usr/bin/aria2c"),
+    )
+
+    installer = Mock()
+
+    monkeypatch.setattr(
+        torrent,
+        "install_aria2c_windows",
+        installer,
+    )
+
+    result = torrent.ensure_aria2c()
+
+    assert result == "/usr/bin/aria2c"
+    installer.assert_not_called()
+
+def test_ensure_aria2c_linux_raises_when_not_installed(monkeypatch):
+    monkeypatch.setattr(
+        torrent.sys,
+        "platform",
+        "linux",
+    )
+
+    monkeypatch.setattr(
+        torrent,
+        "find_aria2c",
+        Mock(return_value=None),
+    )
+
+    installer = Mock()
+
+    monkeypatch.setattr(
+        torrent,
+        "install_aria2c_windows",
+        installer,
+    )
+
+    with pytest.raises(
+        RuntimeError,
+        match="aria2c required but not installed",
+    ):
+        torrent.ensure_aria2c()
+
+    installer.assert_not_called()
 
 def test_ensure_aria2c_passes_custom_logger(monkeypatch):
     monkeypatch.setattr(