Print chats when a test failed (#3937)

* Print chats after a test failed again

E.g.
```
========== Chats of bob: ==========
Single#Chat#10: alice@example.org [alice@example.org]
--------------------------------------------------------------------------------
Msg#10:  (Contact#Contact#10): hellooo [FRESH]
Msg#11:  (Contact#Contact#10): hellooo without mailing list [FRESH]
--------------------------------------------------------------------------------

========== Chats of alice: ==========
Single#Chat#10: bob@example.net [bob@example.net]
--------------------------------------------------------------------------------
Msg#10: Me (Contact#Contact#Self): hellooo  √
Msg#11: Me (Contact#Contact#Self): hellooo without mailing list  √
--------------------------------------------------------------------------------
```

I found this very useful sometimes, so, let's try to re-introduce it (it
was removed in #3449)

* Add failing test for TestContext::drop()

* Do not panic in TestContext::drop() if runtime is dropped

Co-authored-by: link2xt <link2xt@testrun.org>

src/test_utils.rs

@@ -14,6 +14,7 @@ use chat::ChatItem;
 use once_cell::sync::Lazy;
 use rand::Rng;
 use tempfile::{tempdir, TempDir};
+use tokio::runtime::Handle;
 use tokio::sync::RwLock;
 use tokio::task;
 
@@ -263,7 +264,6 @@ impl TestContext {
         Self::builder().configure_fiona().build().await
     }
 
-    #[allow(dead_code)]
     /// Print current chat state.
     pub async fn print_chats(&self) {
         println!("\n========== Chats of {}: ==========", self.name());
@@ -702,6 +702,19 @@ impl Deref for TestContext {
     }
 }
 
+impl Drop for TestContext {
+    fn drop(&mut self) {
+        task::block_in_place(move || {
+            if let Ok(handle) = Handle::try_current() {
+                // Print the chats if runtime still exists.
+                handle.block_on(async move {
+                    self.print_chats().await;
+                });
+            }
+        });
+    }
+}
+
 pub enum LogEvent {
     /// Logged event.
     Event(Event),
@@ -1079,4 +1092,12 @@ mod tests {
         bob.ctx.emit_event(EventType::Info("there".into()));
         // panic!("Both fail");
     }
+
+    /// Checks that dropping the `TestContext` after the runtime does not panic,
+    /// e.g. that `TestContext::drop` does not assume the runtime still exists.
+    #[test]
+    fn test_new_test_context() {
+        let runtime = tokio::runtime::Runtime::new().expect("unable to create tokio runtime");
+        runtime.block_on(TestContext::new());
+    }
 }