test,readline: improve tab completion coverage

test/parallel/test-readline-tab-complete.js

@@ -31,23 +31,23 @@ common.skipIfDumbTerminal();
     const width = getStringWidth(char) - 1;
 
     class FakeInput extends EventEmitter {
-    columns = ((width + 1) * 10 + (lineBreak ? 0 : 10)) * 3
+      columns = ((width + 1) * 10 + (lineBreak ? 0 : 10)) * 3
 
-    write = common.mustCall((data) => {
-      output += data;
-    }, 6)
+      write = common.mustCall((data) => {
+        output += data;
+      }, 6)
 
-    resume() {}
-    pause() {}
-    end() {}
+      resume() {}
+      pause() {}
+      end() {}
     }
 
     const fi = new FakeInput();
     const rli = new readline.Interface({
       input: fi,
       output: fi,
       terminal: true,
-      completer: completer
+      completer: common.mustCallAtLeast(completer),
     });
 
     const last = '\r\nFirst group\r\n\r\n' +
@@ -68,3 +68,35 @@ common.skipIfDumbTerminal();
     rli.close();
   });
 });
+
+{
+  let output = '';
+  class FakeInput extends EventEmitter {
+    columns = 80
+
+    write = common.mustCall((data) => {
+      output += data;
+    }, 1)
+
+    resume() {}
+    pause() {}
+    end() {}
+  }
+
+  const fi = new FakeInput();
+  const rli = new readline.Interface({
+    input: fi,
+    output: fi,
+    terminal: true,
+    completer:
+        common.mustCallAtLeast((_, cb) => cb(new Error('message'))),
+  });
+
+  rli.on('line', common.mustNotCall());
+  fi.emit('data', '\t');
+  queueMicrotask(() => {
+    assert.match(output, /^Tab completion error: Error: message/);
+    output = '';
+  });
+  rli.close();
+}