Benchmark Tests: improve error reporting.

When a benchmark test was failing, there was very little info available
to investigate it. Now report the stdout/stderr generated by the failing
command.

tests/performance/api/__init__.py

@@ -2,7 +2,7 @@
 #
 # SPDX-License-Identifier: Apache-2.0
 
-from .environment import TestEnvironment
+from .environment import TestFailure, TestEnvironment
 from .device import TestDevice, TestMachine
 from .config import TestEntry, TestQueue, TestConfig
 from .test import Test, TestCollection

tests/performance/api/config.py

@@ -31,7 +31,10 @@ class TestEntry:
     device_id: str = 'CPU'
     device_name: str = 'Unknown CPU'
     status: str = 'queued'
+    # Short, single-line error.
     error_msg: str = ''
+    # More detailed error info, potentially multi-lines.
+    exception_msg: str = ''
     output: dict = field(default_factory=dict)
     benchmark_type: str = 'comparison'
 

tests/performance/api/environment.py

@@ -21,6 +21,20 @@ from .config import TestConfig
 from .device import TestMachine
 
 
+class TestFailure(Exception):
+    def __init__(self, *args, message, output_lines=[], **kwargs):
+        super().__init__(message, *args)
+        self.message = message
+        self.output_lines = output_lines
+
+    def __str__(self):
+        msg = self.message
+        if self.output_lines:
+            msg += f":\n{'': <10} | "
+            msg += f"\n{'': <10} | ".join(l.rstrip(' \r\n\t') for l in self.output_lines)
+        return msg
+
+
 class TestEnvironment:
     def __init__(self, blender_git_dir: pathlib.Path, base_dir: pathlib.Path):
         self.blender_git_dir = blender_git_dir
@@ -223,7 +237,7 @@ class TestEnvironment:
 
         # Raise error on failure
         if proc.returncode != 0 and not silent:
-            raise Exception("Error executing command")
+            raise TestFailure(message="Error executing command", output_lines=lines)
 
         return lines