[840] - Test case for operators. (#841)

* [840] - Test case for operators.

* Move import to the head of file and add test_setting.

tests/ops/test_elem_operator.py

@@ -0,0 +1,33 @@
+import unittest
+
+from qlib.data import DatasetProvider
+from qlib.tests import TestOperatorData
+from qlib.config import C
+
+
+class TestOperatorDataSetting(TestOperatorData):
+    def test_setting(self):
+        self.assertEqual(len(self.instruments_d), 1)
+        self.assertGreater(len(self.cal), 0)
+
+
+class TestElementOperator(TestOperatorData):
+    def setUp(self) -> None:
+        freq = "day"
+        expressions = [
+            "$change",
+            "Abs($change)",
+        ]
+        columns = ["change", "abs"]
+        self.data = DatasetProvider.expression_calculator(
+            self.inst, self.start_time, self.end_time, freq, expressions, self.spans, C, []
+        )
+        self.data.columns = columns
+
+    def test_abs(self):
+        abs_values = self.data["abs"]
+        self.assertGreater(abs_values[2], 0)
+
+
+if __name__ == "__main__":
+    unittest.main()