test: show pending exception error in napi tests

Shows the result of the wasPending in the error message if the
assertion fails.

Backport-PR-URL: #19265
PR-URL: #18413
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

Author: blairwilcox

test/addons-napi/test_exception/test.js

@@ -20,9 +20,10 @@ const theError = new Error('Some error');
 
   // Test that the exception thrown above was marked as pending
   // before it was handled on the JS side
-  assert.strictEqual(test_exception.wasPending(), true,
-                     'VM was marked as having an exception pending' +
-                     ' when it was allowed through');
+  const exception_pending = test_exception.wasPending();
+  assert.strictEqual(exception_pending, true,
+                     'Exception not pending as expected,' +
+                     ` .wasPending() returned ${exception_pending}`);
 
   // Test that the native side does not capture a non-existing exception
   returnedError = test_exception.returnException(common.mustCall());
@@ -44,7 +45,8 @@ const theError = new Error('Some error');
                      ` ${caughtError} was passed`);
 
   // Test that the exception state remains clear when no exception is thrown
-  assert.strictEqual(test_exception.wasPending(), false,
-                     'VM was not marked as having an exception pending' +
-                     ' when none was allowed through');
+  const exception_pending = test_exception.wasPending();
+  assert.strictEqual(exception_pending, false,
+                     'Exception state did not remain clear as expected,' +
+                     ` .wasPending() returned ${exception_pending}`);
 }