ENH: Consider warnings as errors when running pytest

Consider warnings as errors when running `pytest`.

.github/workflows/build_test_deploy.yml

@@ -31,6 +31,7 @@ env:
   # Force tox and pytest to use color
   FORCE_COLOR: true
   TEMPLATEFLOW_HOME: /tmp/templateflow
+  NIFREEZE_WERRORS: 1
 
 jobs:
   build:

nireports/conftest.py

@@ -96,3 +96,35 @@ def workdir():
 @pytest.fixture
 def outdir():
     return None if test_output_dir is None else Path(test_output_dir)
+
+
+def pytest_addoption(parser):
+    parser.addoption(
+        "--warnings-as-errors",
+        action="store_true",
+        help="Consider all uncaught warnings as errors.",
+    )
+
+
+@pytest.hookimpl(trylast=True)
+def pytest_sessionfinish(session, exitstatus):
+    have_werrors = os.getenv("NIFREEZE_WERRORS", False)
+    have_werrors = session.config.getoption("--warnings-as-errors", False) or have_werrors
+    if have_werrors:
+        # Check if there were any warnings during the test session
+        reporter = session.config.pluginmanager.get_plugin("terminalreporter")
+        if reporter.stats.get("warnings", None):
+            session.exitstatus = 2
+
+
+@pytest.hookimpl
+def pytest_terminal_summary(terminalreporter, exitstatus, config):
+    have_werrors = os.getenv("NIFREEZE_WERRORS", False)
+    have_werrors = config.getoption("--warnings-as-errors", False) or have_werrors
+    have_warnings = terminalreporter.stats.get("warnings", None)
+    if have_warnings and have_werrors:
+        terminalreporter.ensure_newline()
+        terminalreporter.section("Werrors", sep="=", red=True, bold=True)
+        terminalreporter.line(
+            f"Warnings as errors: Activated.\n{len(have_warnings)} warnings were raised and treated as errors.\n"
+        )

tox.ini

@@ -56,6 +56,7 @@ pass_env =
   CLICOLOR
   CLICOLOR_FORCE
   PYTHON_GIL
+  NIFREEZE_WERRORS
 deps =
   # Waiting on a release
   py313: traits @ git+https://github.com/enthought/traits.git@10954eb