feat(traces): before_span_send hook

posthog/test/tracing/test_config.py

@@ -221,3 +221,52 @@ def test_an_unusable_value_falls_back_rather_than_dropping_every_span(self, valu
         assert resolved.max_attributes_per_span == DEFAULT_MAX_ATTRIBUTES_PER_SPAN
         assert resolved.max_events_per_span == DEFAULT_MAX_EVENTS_PER_SPAN
         assert resolved.max_attribute_value_length == DEFAULT_MAX_ATTRIBUTE_VALUE_LENGTH
+
+
+class TestBeforeSpanSendConfig:
+    def test_accepts_one_hook_or_a_list(self):
+        def hook(span):
+            return span
+
+        assert resolve_traces_config({"before_span_send": hook}).before_span_send == (
+            hook,
+        )
+        assert resolve_traces_config(
+            {"before_span_send": [hook, hook]}
+        ).before_span_send == (hook, hook)
+
+    def test_defaults_to_no_hooks(self):
+        assert resolve_traces_config({}).before_span_send == ()
+
+    def test_skips_falsy_entries_silently(self, caplog):
+        caplog.set_level("WARNING", logger="posthog")
+
+        def hook(span):
+            return span
+
+        resolved = resolve_traces_config({"before_span_send": [None, False, hook]})
+        assert resolved.before_span_send == (hook,)
+        assert not caplog.records
+
+    def test_ignores_and_warns_about_entries_that_are_not_callable(self, caplog):
+        caplog.set_level("WARNING", logger="posthog")
+
+        def hook(span):
+            return span
+
+        resolved = resolve_traces_config({"before_span_send": ["scrub", hook]})
+        assert resolved.before_span_send == (hook,)
+        assert any("1 of 2" in r.getMessage() for r in caplog.records)
+
+    def test_a_hook_whose_truthiness_raises_is_still_resolved(self):
+        class Hook:
+            def __bool__(self):
+                raise RuntimeError("no")
+
+            def __call__(self, span):
+                return span
+
+        hook = Hook()
+        assert resolve_traces_config({"before_span_send": hook}).before_span_send == (
+            hook,
+        )