adding basic tests for smbus

tests/test_sgp.py

@@ -0,0 +1,11 @@
+from .context import sgp30
+
+from mock_smbus2 import MockSMBus
+import unittest
+class BasicTestSuite(unittest.TestCase):
+    """Basic test cases."""
+    def setUp(self):
+        self.bus = MockSMBus()
+    def test_init(self):
+        b=sgp30.sgp30.Sgp30(self.bus)
+        b.init_sgp()