feat: raising error if plot image cannot be obtained (#3559)

* feat: raise exception if file is not found.

* feat: improving error message

* chore: adding changelog file 3559.miscellaneous.md [dependabot-skip]

* tests: adding screenshot testing

* fix: tests

---------

Co-authored-by: pyansys-ci-bot <[email protected]>

doc/changelog.d/3559.miscellaneous.md

@@ -0,0 +1 @@
+feat: raising error if plot image cannot be obtained

src/ansys/mapdl/core/mapdl_core.py

@@ -2359,12 +2359,15 @@ def _cleanup_loggers(self):
             logger.std_out_handler.close()
             logger.std_out_handler = None
 
+    def is_png_found(self, text: str) -> bool:
+        # findall returns None if there is no match
+        return PNG_IS_WRITTEN_TO_FILE.findall(text) is not None
+
     def _get_plot_name(self, text: str) -> str:
         """Obtain the plot filename."""
-        self._log.debug(text)
-        png_found = PNG_IS_WRITTEN_TO_FILE.findall(text)
+        self._log.debug(f"Output from terminal used to find plot name: {text}")
 
-        if png_found:
+        if self.is_png_found(text):
             # flush graphics writer
             previous_device = self.file_type_for_plots
             self.show("CLOSE", mute=True)
@@ -2377,9 +2380,16 @@ def _get_plot_name(self, text: str) -> str:
             if os.path.isfile(filename):
                 return filename
             else:  # pragma: no cover
-                self._log.error("Unable to find screenshot at %s", filename)
+                raise MapdlRuntimeError("Unable to find screenshot at %s", filename)
         else:
-            self._log.error("Unable to find file in MAPDL command output.")
+            raise MapdlRuntimeError(
+                "Unable to find plotted file in MAPDL command output. "
+                "One possible reason is that the graphics device is not correct. "
+                "Please check you are using FULL graphics device. "
+                "For example:\n"
+                ">>> mapdl.graphics('FULL')"
+                f"\nThe text output from MAPDL is:\n{text}"
+            )
 
     def _display_plot(self, filename: str) -> None:
         """Display the last generated plot (*.png) from MAPDL"""

tests/test_plotting.py

@@ -22,6 +22,7 @@
 
 """Unit tests regarding plotting."""
 import os
+from unittest.mock import patch
 
 import numpy as np
 import pytest
@@ -31,7 +32,7 @@
 if not has_dependency("pyvista"):
     pytest.skip(allow_module_level=True)
 
-from ansys.mapdl.core.errors import ComponentDoesNotExits
+from ansys.mapdl.core.errors import ComponentDoesNotExits, MapdlRuntimeError
 from ansys.mapdl.core.plotting.visualizer import MapdlPlotter
 
 FORCE_LABELS = [["FX", "FY", "FZ"], ["HEAT"], ["CHRG"]]
@@ -1254,3 +1255,28 @@ def test_aplot_quality_fail(mapdl, make_block, quality):
         match="The argument 'quality' can only be an integer between 1 and 10",
     ):
         mapdl.aplot(quality=quality)
+
+
+@patch("ansys.mapdl.core.Mapdl.is_png_found", lambda *args, **kwargs: False)
+def test_plot_path(mapdl, tmpdir):
+    mapdl.graphics("POWER")
+
+    with pytest.raises(
+        MapdlRuntimeError,
+        match="One possible reason is that the graphics device is not correct",
+    ):
+        mapdl.eplot(vtk=False)
+
+
+def test_plot_path_screenshoot(mapdl, cleared, tmpdir):
+    mapdl.graphics("POWER")
+    # mapdl.screenshot is not affected by the device.
+    # It should not raise exceptions
+    scheenshot_path = os.path.join(tmpdir, "screenshot.png")
+    mapdl.screenshot(scheenshot_path)
+
+    assert os.path.exists(scheenshot_path)
+    assert os.path.getsize(scheenshot_path) > 100  # check if it is not empty
+
+    # Returning to previous state.
+    mapdl.graphics("FULL")