diff --git a/test/braintrust/trace/span_filter_test.rb b/test/braintrust/trace/span_filter_test.rb
index e4e135c..051a10e 100644
--- a/test/braintrust/trace/span_filter_test.rb
+++ b/test/braintrust/trace/span_filter_test.rb
@@ -11,9 +11,8 @@ def test_init_with_filter_ai_spans_keeps_ai_spans
     tracer_provider = OpenTelemetry::SDK::Trace::TracerProvider.new
 
     Braintrust.init(
-      api_key: "test-key",
+      api_key: "test-api-key",
       set_global: false,
-      blocking_login: false,
       enable_tracing: true,
       tracer_provider: tracer_provider,
       exporter: exporter,
@@ -214,9 +213,8 @@ def setup_with_filter(filter_ai_spans: false, span_filter_funcs: [])
     tracer_provider = OpenTelemetry::SDK::Trace::TracerProvider.new
 
     Braintrust.init(
-      api_key: "test-key",
+      api_key: "test-api-key",
       set_global: false,
-      blocking_login: false,
       enable_tracing: true,
       tracer_provider: tracer_provider,
       exporter: exporter,
diff --git a/test/braintrust/without_openai_test.rb b/test/braintrust/without_openai_test.rb
index 3e0c14a..4f87cdf 100644
--- a/test/braintrust/without_openai_test.rb
+++ b/test/braintrust/without_openai_test.rb
@@ -16,15 +16,15 @@ def test_core_functionality_without_openai
     skip "Test only runs in without-openai appraisal" if openai_available?
 
     # Test that we can initialize Braintrust without tracing (no OpenAI needed)
+    # Note: "test-api-key" triggers fake auth to avoid HTTP requests
     state = Braintrust.init(
-      api_key: "test-key",
+      api_key: "test-api-key",
       set_global: false,
-      blocking_login: false,
       enable_tracing: false
     )
 
     assert_instance_of Braintrust::State, state
-    assert_equal "test-key", state.api_key
+    assert_equal "test-api-key", state.api_key
   end
 
   def test_openai_require_fails_without_gem
diff --git a/test/test_helper.rb b/test/test_helper.rb
index 61d66cf..b1a0f8f 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -64,6 +64,29 @@
 
 # Test helpers for OpenTelemetry tracing
 module TracingTestHelper
+  # =============================================================================
+  # IMPORTANT: Magic Test API Key
+  # =============================================================================
+  #
+  # When calling Braintrust.init in tests, use api_key: "test-api-key" to trigger
+  # fake authentication that avoids HTTP requests. This magic key is handled in
+  # lib/braintrust/api/internal/auth.rb and returns fake org info immediately.
+  #
+  # Without this magic key, Braintrust.init spawns a background login thread that
+  # can cause WebMock errors after tests complete (orphan thread race condition).
+  #
+  # Example:
+  #   Braintrust.init(api_key: "test-api-key", set_global: false, enable_tracing: true)
+  #
+  # TODO: Future work - move this magic key handling out of production code and into
+  # test helpers instead. Options include:
+  #   1. A test-only initializer that provides org_id directly (skips login entirely)
+  #   2. Dependency injection for the Auth module in tests
+  #   3. Environment-based test mode detection
+  #
+  # See: lib/braintrust/api/internal/auth.rb for the magic key implementation
+  # =============================================================================
+
   # Wrapper for OpenTelemetry test setup
   class OtelTestRig
     attr_reader :tracer_provider, :exporter, :state