diff --git a/src/builtins/mod.rs b/src/builtins/mod.rs
index ef5b9aa..0f5ed81 100644
--- a/src/builtins/mod.rs
+++ b/src/builtins/mod.rs
@@ -27,7 +27,8 @@ lazy_static! {
 
 	numbers::register(&mut m);
 	aggregates::register(&mut m);
-	arrays::register(&mut m);	
+	arrays::register(&mut m);
+	types::register(&mut m);
 
 	m
     };
diff --git a/tests/interpreter/cases/builtins/mod.rs b/tests/interpreter/cases/builtins/mod.rs
new file mode 100644
index 0000000..ef7450f
--- /dev/null
+++ b/tests/interpreter/cases/builtins/mod.rs
@@ -0,0 +1,11 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+use regorus::builtins;
+use regorus::Value;
+
+// Lockdown calls that cannot happen via rego.
+#[test]
+fn type_name_undefined() {
+    assert_eq!(builtins::types::get_type(&Value::Undefined), "undefined");
+}
diff --git a/tests/interpreter/cases/builtins/types.yaml b/tests/interpreter/cases/builtins/types.yaml
new file mode 100644
index 0000000..bc46970
--- /dev/null
+++ b/tests/interpreter/cases/builtins/types.yaml
@@ -0,0 +1,48 @@
+# Copyright (c) Microsoft Corporation.
+# Licensed under the MIT License.
+
+cases:
+  - note: all
+    data: {}
+    modules:
+      - |
+        package test
+
+        items = [
+           [],
+           true,
+           null,
+           0,
+           {},
+           set(),
+           "abc",
+        ]
+
+        results = {
+          "is_array" : [x | x = items[_]; is_array(x)],
+          "is_boolean" : [x | x = items[_]; is_boolean(x)],
+          "is_null" : [x | x = items[_]; is_null(x)],
+          "is_number" : [x | x = items[_]; is_number(x)],
+          "is_object" : [x | x = items[_]; is_object(x)],
+          "is_set" : [x | x = items[_]; is_set(x)],
+          "is_string" : [x | x = items[_]; is_string(x)],
+          "type_names": [n | n = type_name(items[_])],
+        }
+    query: data.test.results
+    want_result:
+      is_array: [[]]
+      is_boolean: [true]
+      is_null: [null]
+      is_number: [0]
+      is_object: [{}]
+      is_set:
+        - set!: []
+      is_string: ["abc"]
+      type_names:
+        - "array"
+        - "boolean"
+        - "null"
+        - "number"
+        - "object"
+        - "set"
+        - "string"
diff --git a/tests/interpreter/cases/mod.rs b/tests/interpreter/cases/mod.rs
index 44c7283..67e9f63 100644
--- a/tests/interpreter/cases/mod.rs
+++ b/tests/interpreter/cases/mod.rs
@@ -2,6 +2,7 @@
 // Licensed under the MIT License.
 
 mod arithmetic;
+mod builtins;
 mod compr;
 mod r#in;
 mod variables;
diff --git a/tests/interpreter/mod.rs b/tests/interpreter/mod.rs
index 514e72c..99cd9f7 100644
--- a/tests/interpreter/mod.rs
+++ b/tests/interpreter/mod.rs
@@ -350,37 +350,6 @@ fn one_yaml() -> Result<()> {
     yaml_test(file.as_str())
 }
 
-/*
-fn run_yaml_tests_in(folder: &str) -> Result<()> {
-    let mut total = 0;
-
-    for entry in WalkDir::new(folder)
-        .follow_links(true)
-        .into_iter()
-        .filter_map(|e| e.ok())
-    {
-        let path = entry
-            .path()
-            .to_str()
-            .ok_or_else(|| anyhow!("failed to convert path to utf8 {:?}", entry.path()))?;
-        if !path.ends_with(".yaml") {
-            continue;
-        }
-
-        total += 1;
-        yaml_test(path)?;
-    }
-
-    println!("{} yaml tests passed.", total);
-    Ok(())
-}
-
-#[test]
-fn run_yaml_tests() -> Result<()> {
-    run_yaml_tests_in("tests/interpreter")
-}
-*/
-
 #[test_resources("tests/interpreter/**/*.yaml")]
 fn run(path: &str) {
     yaml_test(path).unwrap()