diff --git a/tests/codegen/lexicon/defs_no_main_promotion/input.mlf b/tests/codegen/lexicon/defs_no_main_promotion/input.mlf
new file mode 100644
index 0000000..d9427b2
--- /dev/null
+++ b/tests/codegen/lexicon/defs_no_main_promotion/input.mlf
@@ -0,0 +1,13 @@
+/// A simple view of a user profile.
+def type profileView = {
+    did!: Did,
+    handle!: Handle,
+    displayName: string,
+};
+
+/// A detailed view with follower counts.
+def type profileViewDetailed = {
+    did!: Did,
+    handle!: Handle,
+    followersCount: integer,
+};
diff --git a/tests/codegen/lexicon/defs_no_main_promotion/lexicon@defs_no_main_promotion.snap b/tests/codegen/lexicon/defs_no_main_promotion/lexicon@defs_no_main_promotion.snap
new file mode 100644
index 0000000..a030f36
--- /dev/null
+++ b/tests/codegen/lexicon/defs_no_main_promotion/lexicon@defs_no_main_promotion.snap
@@ -0,0 +1,53 @@
+---
+source: tests/codegen_integration.rs
+expression: output.json
+---
+{
+  "$type": "com.atproto.lexicon.schema",
+  "lexicon": 1,
+  "id": "com.example.actor.defs",
+  "defs": {
+    "profileView": {
+      "type": "object",
+      "description": "A simple view of a user profile.",
+      "required": [
+        "did",
+        "handle"
+      ],
+      "properties": {
+        "did": {
+          "type": "string",
+          "format": "did"
+        },
+        "handle": {
+          "type": "string",
+          "format": "handle"
+        },
+        "displayName": {
+          "type": "string"
+        }
+      }
+    },
+    "profileViewDetailed": {
+      "type": "object",
+      "description": "A detailed view with follower counts.",
+      "required": [
+        "did",
+        "handle"
+      ],
+      "properties": {
+        "did": {
+          "type": "string",
+          "format": "did"
+        },
+        "handle": {
+          "type": "string",
+          "format": "handle"
+        },
+        "followersCount": {
+          "type": "integer"
+        }
+      }
+    }
+  }
+}
diff --git a/tests/codegen/lexicon/defs_no_main_promotion/test.toml b/tests/codegen/lexicon/defs_no_main_promotion/test.toml
new file mode 100644
index 0000000..7eca0d6
--- /dev/null
+++ b/tests/codegen/lexicon/defs_no_main_promotion/test.toml
@@ -0,0 +1,4 @@
+[test]
+name = "defs_no_main_promotion"
+description = "In .defs namespaces, no def is promoted to main — even a sole def keeps its name"
+namespace = "com.example.actor.defs"
diff --git a/tests/codegen/lexicon/defs_no_main_promotion/warnings@defs_no_main_promotion.snap b/tests/codegen/lexicon/defs_no_main_promotion/warnings@defs_no_main_promotion.snap
new file mode 100644
index 0000000..23a5161
--- /dev/null
+++ b/tests/codegen/lexicon/defs_no_main_promotion/warnings@defs_no_main_promotion.snap
@@ -0,0 +1,5 @@
+---
+source: tests/codegen_integration.rs
+expression: formatted_warnings
+---
+[]
diff --git a/tests/lexicon_to_mlf/union_refs_as_nsids/input.json b/tests/lexicon_to_mlf/union_refs_as_nsids/input.json
new file mode 100644
index 0000000..8dd8a95
--- /dev/null
+++ b/tests/lexicon_to_mlf/union_refs_as_nsids/input.json
@@ -0,0 +1,26 @@
+{
+  "lexicon": 1,
+  "id": "com.example.unionnsids",
+  "defs": {
+    "main": {
+      "type": "object",
+      "required": ["content"],
+      "properties": {
+        "content": {
+          "type": "union",
+          "refs": [
+            "#textBlock",
+            "com.example.external#imageBlock"
+          ]
+        }
+      }
+    },
+    "textBlock": {
+      "type": "object",
+      "required": ["text"],
+      "properties": {
+        "text": { "type": "string" }
+      }
+    }
+  }
+}
diff --git a/tests/lexicon_to_mlf/union_refs_as_nsids/mlf@union_refs_as_nsids.snap b/tests/lexicon_to_mlf/union_refs_as_nsids/mlf@union_refs_as_nsids.snap
new file mode 100644
index 0000000..4e94aae
--- /dev/null
+++ b/tests/lexicon_to_mlf/union_refs_as_nsids/mlf@union_refs_as_nsids.snap
@@ -0,0 +1,12 @@
+---
+source: tests/lexicon_to_mlf_integration.rs
+expression: output.mlf
+---
+@main
+def type unionnsids = {
+    content!: textBlock | com.example.external.imageBlock,
+};
+
+def type textBlock = {
+    text!: string,
+};
diff --git a/tests/lexicon_to_mlf/union_refs_as_nsids/warnings@union_refs_as_nsids.snap b/tests/lexicon_to_mlf/union_refs_as_nsids/warnings@union_refs_as_nsids.snap
new file mode 100644
index 0000000..87c353b
--- /dev/null
+++ b/tests/lexicon_to_mlf/union_refs_as_nsids/warnings@union_refs_as_nsids.snap
@@ -0,0 +1,5 @@
+---
+source: tests/lexicon_to_mlf_integration.rs
+expression: formatted_warnings
+---
+[]