pytest: add latest fork parameter and exit gracefully upon an invalid fork

pyproject.toml

@@ -15,7 +15,8 @@ console_output_style = "count"
 minversion = "7.0"
 testpaths = ["fillers/example", "fillers/eips/eip3651.py", "fillers/eips/eip3855.py", "fillers/vm/chain_id.py"]
 python_files = "*.py"
+addopts = "-p pytest_plugins.latest_fork"
 markers = [
     "state_test: test cases that implement a single state transition test",
     "blockchain_test: test cases that implement block transition tests",
-]
+]

src/ethereum_test_forks/__init__.py

@@ -25,6 +25,7 @@
 )
 from .forks.upcoming import Cancun
 from .helpers import (
+    InvalidForkError,
     fork_only,
     forks_from,
     forks_from_until,
@@ -44,6 +45,7 @@
     "Frontier",
     "GrayGlacier",
     "Homestead",
+    "InvalidForkError",
     "Istanbul",
     "London",
     "Merge",

src/ethereum_test_forks/helpers.py

@@ -21,6 +21,11 @@ def __init__(self):
 latest_fork_resolver = LatestForkResolver()
 
 
+class InvalidForkError(Exception):
+    def __init__(self, message):
+        super().__init__(message)
+
+
 def set_latest_fork(fork: Fork) -> None:
     """
     Sets the latest fork
@@ -37,7 +42,7 @@ def set_latest_fork_by_name(fork_name: str) -> None:
     elif fork_name in upcoming.__dict__:
         set_latest_fork(upcoming.__dict__[fork_name])
     else:
-        raise Exception(f'fork "{fork_name}" not found')
+        raise InvalidForkError(f'fork "{fork_name}" not found')
 
 
 def get_parent_fork(fork: Fork) -> Fork:

src/pytest_plugins/latest_fork.py

@@ -0,0 +1,62 @@
+import pytest
+
+from ethereum_test_forks import (
+    InvalidForkError,
+    set_latest_fork_by_name,
+)
+
+
+def pytest_addoption(parser):
+    """
+    Adds command-line options to pytest.
+    """
+    group = parser.getgroup("forks", "Arguments defining fork configuration")
+    group.addoption(
+        "--latest-fork",
+        action="store",
+        dest="latest_fork",
+        default=None,
+        help="Latest fork used to fill tests",
+    )
+
+
+def pytest_configure(config):
+    """
+    Check parameters and make session-wide configuration changes, such as
+    setting the latest fork.
+    """
+    latest_fork = config.getoption("latest_fork")
+    if latest_fork is not None:
+        try:
+            set_latest_fork_by_name(latest_fork)
+        except InvalidForkError as e:
+            pytest.exit(f"Error applying --latest-fork={latest_fork}: {e}.")
+        except Exception as e:
+            raise e
+    return None
+
+
+@pytest.hookimpl(trylast=True)
+def pytest_report_header(config, start_path):
+    """A pytest hook called to obtain the report header."""
+    bold = "\033[1m"
+    warning = "\033[93m"
+    reset = "\033[39;49m"
+    if config.getoption("latest_fork") is None:
+        header = [
+            (
+                bold
+                + warning
+                + "Only executing fillers with stable/deployed forks: "
+                "Specify an upcoming fork via --latest-fork=fork to "
+                "run experimental fillers." + reset
+            )
+        ]
+    else:
+        header = [
+            (
+                bold + "Executing fillers up to and including "
+                f"{config.getoption('latest_fork')}." + reset
+            ),
+        ]
+    return header