tests: Add tests for configurable warnings

This adds multiple tests for custom plugin warnings and core warnings,
providing checks for both cases which should cause warnings and errors
when configured as fatal.

tests/frontend/configurable_warnings.py

+import pytest
+import os
+
+from buildstream.plugin import CoreWarnings
+from buildstream._exceptions import ErrorDomain, LoadErrorReason
+from buildstream import _yaml
+from tests.testutils.runcli import cli
+
+TOP_DIR = os.path.join(
+    os.path.dirname(os.path.realpath(__file__)),
+    "configuredwarning"
+)
+
+
+def get_project(fatal_warnings):
+    return {
+        "name": "test",
+        "element-path": "elements",
+        "plugins": [
+            {
+                "origin": "local",
+                "path": "plugins",
+                "elements": {
+                    "warninga": 0,
+                    "warningb": 0,
+                    "corewarn": 0,
+                }
+            }
+        ],
+        "fatal-warnings": fatal_warnings
+    }
+
+
+def build_project(datafiles, fatal_warnings):
+    project_path = os.path.join(datafiles.dirname, datafiles.basename)
+
+    project = get_project(fatal_warnings)
+
+    _yaml.dump(project, os.path.join(project_path, "project.conf"))
+
+    return project_path
+
+
+@pytest.mark.datafiles(TOP_DIR)
+@pytest.mark.parametrize("element_name, fatal_warnings, expect_fatal, error_domain", [
+    ("corewarn.bst", [CoreWarnings.OVERLAPS], True, ErrorDomain.STREAM),
+    ("warninga.bst", ["warninga:warning-a"], True, ErrorDomain.STREAM),
+    ("warningb.bst", ["warningb:warning-b"], True, ErrorDomain.STREAM),
+    ("corewarn.bst", [], False, None),
+    ("warninga.bst", [], False, None),
+    ("warningb.bst", [], False, None),
+    ("corewarn.bst", "true", True, ErrorDomain.STREAM),
+    ("warninga.bst", "true", True, ErrorDomain.STREAM),
+    ("warningb.bst", "true", True, ErrorDomain.STREAM),
+    ("warninga.bst", [CoreWarnings.OVERLAPS], False, None),
+    ("warningb.bst", [CoreWarnings.OVERLAPS], False, None),
+])
+def test_fatal_warnings(cli, datafiles, element_name,
+                        fatal_warnings, expect_fatal, error_domain):
+    project_path = build_project(datafiles, fatal_warnings)
+
+    result = cli.run(project=project_path, args=["build", element_name])
+    if expect_fatal:
+        result.assert_main_error(error_domain, None, "Expected fatal execution")
+    else:
+        result.assert_success("Unexpected fatal execution")

tests/frontend/configuredwarning/elements/corewarn.bst

+kind: corewarn
\ No newline at end of file

tests/frontend/configuredwarning/elements/warninga.bst

+kind: warninga

tests/frontend/configuredwarning/elements/warningb.bst

+kind: warningb

tests/frontend/configuredwarning/plugins/corewarn.py

+from buildstream import Element
+from buildstream.plugin import CoreWarnings
+
+
+class CoreWarn(Element):
+    def configure(self, node):
+        pass
+
+    def preflight(self):
+        pass
+
+    def get_unique_key(self):
+        pass
+
+    def get_warnings(self):
+        return []  # CoreWarnings should be included regardless of plugins.
+
+    def configure_sandbox(self, sandbox):
+        pass
+
+    def stage(self, sandbox):
+        pass
+
+    def assemble(self, sandbox):
+        self.warn("Testing: CoreWarning produced during assemble",
+                  warning_token=CoreWarnings.OVERLAPS)
+
+
+def setup():
+    return CoreWarn

tests/frontend/configuredwarning/plugins/warninga.py

+from buildstream import Element
+
+WARNING_A = "warning-a"
+
+
+class WarningA(Element):
+    def configure(self, node):
+        pass
+
+    def preflight(self):
+        pass
+
+    def get_unique_key(self):
+        pass
+
+    def configure_sandbox(self, sandbox):
+        pass
+
+    def stage(self, sandbox):
+        pass
+
+    def assemble(self, sandbox):
+        self.warn("Testing: warning-a produced during assemble", warning_token=WARNING_A)
+
+
+def setup():
+    return WarningA

tests/frontend/configuredwarning/plugins/warningb.py

+from buildstream import Element
+
+WARNING_B = "warning-b"
+
+
+class WarningB(Element):
+    def configure(self, node):
+        pass
+
+    def preflight(self):
+        pass
+
+    def get_unique_key(self):
+        pass
+
+    def configure_sandbox(self, sandbox):
+        pass
+
+    def stage(self, sandbox):
+        pass
+
+    def assemble(self, sandbox):
+        self.warn("Testing: warning-b produced during assemble", warning_token=WARNING_B)
+
+
+def setup():
+    return WarningB

tests/frontend/configuredwarning/project.conf

+name: test
+element-path: elements
+plugins:
+- origin: local
+  path: element_plugins
+  elements:
+    warninga: 0
+    warningb: 0