chore(pytest): fail fast on typos in notimpl, notyet, and never marks

A typo in one of our custom marks would just lead to a test
failure (usually) because a test that we expected to xfail wasn't
xfailed.

This is annoying because a) it's surprising and b) you have to run
possibly the whole test suite to hit it (and then you have to figure out
why).

I added a collection hook to flag any typos in the arguments to our
custom marks, and it spits them all out, along with path and test name,
then aborts the test run altogether.

ibis/backends/conftest.py

@@ -121,6 +121,8 @@
     'ibis/backends/tests/test_window.py',
 ]
 
+ALL_BACKENDS = set(_get_backend_names())
+
 
 @pytest.fixture(scope='session')
 def script_directory() -> Path:
@@ -279,7 +281,6 @@ def pytest_ignore_collect(path, config):
 
 
 def pytest_collection_modifyitems(session, config, items):
-    # add the backend marker to any tests are inside "ibis/backends"
     all_backends = _get_backend_names()
     additional_markers = []
 
@@ -288,7 +289,20 @@ def pytest_collection_modifyitems(session, config, items):
     except ImportError:
         pyspark = None
 
+    unrecognized_backends = set()
     for item in items:
+        # Yell loudly if unrecognized backend in notimpl, notyet or never
+        for name in ("notimpl", "notyet", "never"):
+            for mark in item.iter_markers(name=name):
+                if backend := set(util.promote_list(mark.args[0])).difference(
+                    ALL_BACKENDS
+                ):
+                    unrecognized_backends.add(
+                        f"""Unrecognize backend(s) {backend} passed to {name} marker in
+{item.path}::{item.originalname}"""
+                    )
+
+        # add the backend marker to any tests are inside "ibis/backends"
         parts = item.path.parts
         backend = _get_backend_from_parts(parts)
         if backend is not None and backend in all_backends:
@@ -305,6 +319,7 @@ def pytest_collection_modifyitems(session, config, items):
             if not any(item.iter_markers(name="benchmark")):
                 item.add_marker(pytest.mark.core)
 
+        # skip or xfail pyspark tests that run afoul of our non-ancient stack
         for _ in item.iter_markers(name="pyspark"):
             if not isinstance(item, pytest.DoctestItem):
                 additional_markers.append(
@@ -329,6 +344,9 @@ def pytest_collection_modifyitems(session, config, items):
                     )
                 )
 
+    if unrecognized_backends:
+        raise pytest.PytestCollectionWarning("\n" + "\n".join(unrecognized_backends))
+
     for item, markers in additional_markers:
         for marker in markers:
             item.add_marker(marker)