1 files changed, 66 insertions, 0 deletions
diff --git a/library/core/tests/error.rs b/library/core/tests/error.rs
new file mode 100644
index 000000000..cb7cb5441
--- /dev/null
+++ b/library/core/tests/error.rs
@@ -0,0 +1,66 @@
+use core::error::{request_value, request_ref, Request};
+
+// Test the `Request` API.
+#[derive(Debug)]
+struct SomeConcreteType {
+    some_string: String,
+}
+
+impl std::fmt::Display for SomeConcreteType {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "A")
+    }
+}
+
+impl std::error::Error for SomeConcreteType {
+    fn provide<'a>(&'a self, request: &mut Request<'a>) {
+        request
+            .provide_ref::<String>(&self.some_string)
+            .provide_ref::<str>(&self.some_string)
+            .provide_value_with::<String>(|| "bye".to_owned());
+    }
+}
+
+// Test the Error.provide and request mechanisms with a by-reference trait object.
+#[test]
+fn test_error_generic_member_access() {
+    let obj = &SomeConcreteType { some_string: "hello".to_owned() };
+
+    assert_eq!(request_ref::<String>(&*obj).unwrap(), "hello");
+    assert_eq!(request_value::<String>(&*obj).unwrap(), "bye");
+    assert_eq!(request_value::<u8>(&obj), None);
+}
+
+// Test the Error.provide and request mechanisms with a by-reference trait object.
+#[test]
+fn test_request_constructor() {
+    let obj: &dyn std::error::Error = &SomeConcreteType { some_string: "hello".to_owned() };
+
+    assert_eq!(request_ref::<String>(&*obj).unwrap(), "hello");
+    assert_eq!(request_value::<String>(&*obj).unwrap(), "bye");
+    assert_eq!(request_value::<u8>(&obj), None);
+}
+
+// Test the Error.provide and request mechanisms with a boxed trait object.
+#[test]
+fn test_error_generic_member_access_boxed() {
+    let obj: Box<dyn std::error::Error> =
+        Box::new(SomeConcreteType { some_string: "hello".to_owned() });
+
+    assert_eq!(request_ref::<String>(&*obj).unwrap(), "hello");
+    assert_eq!(request_value::<String>(&*obj).unwrap(), "bye");
+
+    // NOTE: Box<E> only implements Error when E: Error + Sized, which means we can't pass a
+    // Box<dyn Error> to request_value.
+    //assert_eq!(request_value::<String>(&obj).unwrap(), "bye");
+}
+
+// Test the Error.provide and request mechanisms with a concrete object.
+#[test]
+fn test_error_generic_member_access_concrete() {
+    let obj = SomeConcreteType { some_string: "hello".to_owned() };
+
+    assert_eq!(request_ref::<String>(&obj).unwrap(), "hello");
+    assert_eq!(request_value::<String>(&obj).unwrap(), "bye");
+    assert_eq!(request_value::<u8>(&obj), None);
+}