test: show pending exception error in napi tests

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,
+                     'Expected exception to be pending, but' +
+                     `it was marked as ${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,
+                     'Expected no exception to be pending, but' +
+                     ` it was marked as ${exception_pending}`);
 }