Fix Deno display_data to use broadcast API (#7)

* Fix Deno display_data to use broadcast API

The Deno.jupyter.html tagged template doesn't emit display_data messages.
Use Deno.jupyter.broadcast("display_data", ...) which is proven to work.
Also clarify evcxr requires trait impl for display_data.

* Add execute_stderr test (Tier 1)

Tests that kernels can output to stderr stream correctly.

Author: rgbkrk

src/snippets.rs

@@ -109,7 +109,7 @@ impl LanguageSnippets {
             completion_var: "test_variable_for_completion",
             completion_setup: "let test_variable_for_completion = 42;",
             completion_prefix: "test_variable_for_",
-            display_data_code: r#"println!("EVCXR_BEGIN_CONTENT text/html\n<b>bold</b>\nEVCXR_END_CONTENT")"#,
+            display_data_code: "// evcxr requires evcxr_display trait impl for display_data",
             update_display_data_code: "// evcxr doesn't support update_display_data (no display_id)",
         }
     }
@@ -150,7 +150,7 @@ impl LanguageSnippets {
             completion_var: "testVariableForCompletion",
             completion_setup: "const testVariableForCompletion = 42",
             completion_prefix: "testVariableFor",
-            display_data_code: "Deno.jupyter.html`<b>bold</b>`",
+            display_data_code: r#"await Deno.jupyter.broadcast("display_data", { data: { "text/html": "<b>bold</b>" }, metadata: {}, transient: {} })"#,
             update_display_data_code: r#"await Deno.jupyter.broadcast("display_data", { data: { "text/html": "<b>initial</b>" }, metadata: {}, transient: { display_id: "test_update" } }); await Deno.jupyter.broadcast("update_display_data", { data: { "text/html": "<b>updated</b>" }, metadata: {}, transient: { display_id: "test_update" } })"#,
         }
     }

src/tests.rs

@@ -126,6 +126,37 @@ fn test_execute_stdout(
     })
 }
 
+fn test_execute_stderr(
+    kernel: &mut KernelUnderTest,
+) -> Pin<Box<dyn Future<Output = TestResult> + Send + '_>> {
+    Box::pin(async move {
+        let code = kernel.snippets().print_stderr.to_string();
+        match kernel.execute_and_collect(&code).await {
+            Ok((_, iopub)) => {
+                let has_stderr = iopub.iter().any(|msg| {
+                    matches!(
+                        &msg.content,
+                        JupyterMessageContent::StreamContent(StreamContent {
+                            name: jupyter_protocol::messaging::Stdio::Stderr,
+                            text,
+                        }) if text.contains("error")
+                    )
+                });
+                if has_stderr {
+                    TestResult::Pass
+                } else {
+                    TestResult::Fail { kind: None,
+                        reason: "No stderr containing 'error'".to_string(),
+                    }
+                }
+            }
+            Err(e) => TestResult::Fail { kind: None,
+                reason: e.to_string(),
+            },
+        }
+    })
+}
+
 fn test_execute_reply_ok(
     kernel: &mut KernelUnderTest,
 ) -> Pin<Box<dyn Future<Output = TestResult> + Send + '_>> {
@@ -845,6 +876,13 @@ pub fn all_tests() -> Vec<ConformanceTest> {
             message_type: "execute_request",
             run: test_execute_stdout,
         },
+        ConformanceTest {
+            name: "execute_stderr",
+            category: TestCategory::Tier1Basic,
+            description: "Execute code that prints to stderr produces stream message",
+            message_type: "stream",
+            run: test_execute_stderr,
+        },
         ConformanceTest {
             name: "execute_reply_ok",
             category: TestCategory::Tier1Basic,