Have ForwardModelRunner validate executable_file earlier

This commit fixes the issue where the ForwardModelRunner on the job_runner side would crash when validating the existence of a ForwardModelStep executable; causing the drivers to hang while waiting for a never coming return code from JobRunner.

src/_ert/forward_model_runner/io/__init__.py

@@ -6,7 +6,7 @@ def cond_unlink(file):
         os.unlink(file)
 
 
-def assert_file_executable(fname):
+def check_executable(fname) -> str:
     """The function raises an IOError if the given file is either not a file or
     not an executable.
 
@@ -17,7 +17,7 @@ def assert_file_executable(fname):
 
     """
     if not fname:
-        raise IOError("No executable provided!")
+        return "No executable provided!"
     fname = os.path.expanduser(fname)
 
     potential_executables = [os.path.abspath(fname)]
@@ -28,7 +28,7 @@ def assert_file_executable(fname):
         ]
 
     if not any(map(os.path.isfile, potential_executables)):
-        raise IOError(f"{fname} is not a file!")
+        return f"{fname} is not a file!"
 
     if not any(os.access(fn, os.X_OK) for fn in potential_executables):
-        raise IOError(f"{fname} is not an executable!")
+        return f"{fname} is not an executable!"

src/_ert/forward_model_runner/job.py

@@ -14,7 +14,7 @@
 
 from psutil import AccessDenied, NoSuchProcess, Process, TimeoutExpired, ZombieProcess
 
-from .io import assert_file_executable
+from .io import check_executable
 from .reporting.message import (
     Exited,
     MemoryStatus,
@@ -97,10 +97,7 @@ def run(self):
 
         yield start_message
 
-        executable = self.job_data.get("executable")
-        assert_file_executable(executable)
-
-        arg_list = [executable]
+        arg_list = [self.job_data.get("executable")]
         if self.job_data.get("argList"):
             arg_list += self.job_data["argList"]
 
@@ -313,6 +310,9 @@ def _check_job_files(self):
         ):
             os.unlink(self.job_data.get("error_file"))
 
+        if executable_error := check_executable(self.job_data.get("executable")):
+            errors.append(str(executable_error))
+
         return errors
 
     def _check_target_file_is_written(self, target_file_mtime: int, timeout=5):

tests/unit_tests/forward_model_runner/test_job.py

@@ -219,9 +219,9 @@ def test_run_with_defined_executable_but_missing():
         0,
     )
 
-    with pytest.raises(IOError):
-        for _ in job.run():
-            pass
+    start_message = next(job.run())
+    assert isinstance(start_message, Start)
+    assert "this/is/not/a/file is not a file" in start_message.error_message
 
 
 @pytest.mark.usefixtures("use_tmpdir")
@@ -265,10 +265,9 @@ def test_run_with_defined_executable_no_exec_bit():
         },
         0,
     )
-
-    with pytest.raises(IOError):
-        for _ in job.run():
-            pass
+    start_message = next(job.run())
+    assert isinstance(start_message, Start)
+    assert "foo is not an executable" in start_message.error_message
 
 
 def test_init_job_no_std():