launch_external_viewer: Use full path when opening the file in a web …

…browser (#3647)

pygmt/helpers/utils.py

@@ -12,6 +12,7 @@
 import time
 import webbrowser
 from collections.abc import Iterable, Mapping, Sequence
+from pathlib import Path
 from typing import Any, Literal
 
 import xarray as xr
@@ -580,7 +581,7 @@ def launch_external_viewer(fname: str, waiting: float = 0):
         case "win32":  # Windows
             os.startfile(fname)  # type:ignore[attr-defined] # noqa: S606
         case _:  # Fall back to the browser if can't recognize the operating system.
-            webbrowser.open_new_tab(f"file://{fname}")
+            webbrowser.open_new_tab(f"file://{Path(fname).resolve()}")
     if waiting > 0:
         # Preview images will be deleted when a GMT modern-mode session ends, but the
         # external viewer program may take a few seconds to open the images.

pygmt/tests/test_helpers.py

@@ -194,13 +194,16 @@ def test_launch_external_viewer_win32():
         mock_startfile.assert_called_once_with("preview.png")
 
 
-def test_launch_external_viewer_unknown_os():
+@pytest.mark.parametrize("fname", ["preview.png", "/full/path/to/preview.png"])
+def test_launch_external_viewer_unknown_os(fname):
     """
     Test that launch_external_viewer uses the webbrowser module as a fallback.
     """
     with (
-        patch("webbrowser.open_new_tab") as mock_open,
         patch("sys.platform", "unknown"),
+        patch("webbrowser.open_new_tab") as mock_open,
     ):
-        launch_external_viewer("preview.png")
-        mock_open.assert_called_once_with("file://preview.png")
+        launch_external_viewer(fname)
+        fullpath = Path(fname).resolve()
+        assert fullpath.is_absolute()
+        mock_open.assert_called_once_with(f"file://{fullpath}")