Add explicit test coverage for 'LoadJobConfig.skip_leading_rows'.

Note question posted to issue #5093:  should 'max_bad_rows' and
'skip_leading_rows' match in how the mangle / parse the value in the
resource?  Docs say it is an integer.

bigquery/google/cloud/bigquery/job.py

@@ -981,10 +981,12 @@ def max_bad_records(self):
         See
         https://cloud.google.com/bigquery/docs/reference/rest/v2/jobs#configuration.load.maxBadRecords
         """
+        # XXX: should this coerce from str, like 'skip_leading_rows' below?
         return self._get_sub_prop('maxBadRecords')
 
     @max_bad_records.setter
     def max_bad_records(self, value):
+        # XXX: should this coerce to str, like 'skip_leading_rows' below?
         self._set_sub_prop('maxBadRecords', value)
 
     @property

bigquery/tests/unit/test_job.py

@@ -1333,6 +1333,31 @@ def test_quote_character_setter(self):
         self.assertEqual(
             config._properties['load']['quote'], quote_character)
 
+    def test_skip_leading_rows_missing(self):
+        config = self._get_target_class()()
+        self.assertIsNone(config.skip_leading_rows)
+
+    def test_skip_leading_rows_hit_w_str(self):
+        skip_leading_rows = 1
+        config = self._get_target_class()()
+        config._properties['load']['skipLeadingRows'] = str(skip_leading_rows)
+        self.assertEqual(config.skip_leading_rows, skip_leading_rows)
+
+    def test_skip_leading_rows_hit_w_integer(self):
+        skip_leading_rows = 1
+        config = self._get_target_class()()
+        config._properties['load']['skipLeadingRows'] = skip_leading_rows
+        self.assertEqual(config.skip_leading_rows, skip_leading_rows)
+
+    def test_skip_leading_rows_setter(self):
+        skip_leading_rows = 1
+        config = self._get_target_class()()
+        config.skip_leading_rows = skip_leading_rows
+        self.assertEqual(
+            config._properties['load']['skipLeadingRows'],
+            # XXX: Should this really be a str?
+            str(skip_leading_rows))
+
     def test_schema(self):
         from google.cloud.bigquery.schema import SchemaField
         config = self._get_target_class()()