diff --git a/tests/mock_smbus2.py b/tests/mock_smbus2.py
index 6df03e3..dcfac70 100644
--- a/tests/mock_smbus2.py
+++ b/tests/mock_smbus2.py
@@ -18,6 +18,8 @@ answers = {
 class MockSMBus:
     def __init__(s):
         s.status=None
+        s.last=None
+        s.addr=None
 
     def i2c_rdwr(s,*msgs):
         for m in msgs:
@@ -25,6 +27,12 @@ class MockSMBus:
                 s._process_read(m)
             else:
                 s._process_write(m)
+
+    def write_byte(s,addr,data):
+        s.status=None
+        s.addr=addr
+        s.last=data
+
     def _process_read(s,msg):
         if s.status == None:
             raise AssertionError("tired to read before write")
@@ -32,4 +40,5 @@ class MockSMBus:
             msg.buf[i]=chr(s.status[i])
     def _process_write(s,msg):
         s.status = answers[tuple(msg)]
+        s.last=msg
     
diff --git a/tests/test_sgp.py b/tests/test_sgp.py
index 66f382f..d8623c4 100644
--- a/tests/test_sgp.py
+++ b/tests/test_sgp.py
@@ -11,10 +11,16 @@ class TestConstructor(unittest.TestCase):
         b=sgp30.sgp30.Sgp30(self.bus)
         b.init_sgp()
 
-class SimpleTest(unittest.TestCase):
+    def test_general_call(self):
+        b=sgp30.sgp30.Sgp30(self.bus)
+        b.i2c_geral_call()
+        self.assertEqual(self.bus.addr,0)
+        self.assertEqual(self.bus.last,0x06)
+
+class SimpleReadTests(unittest.TestCase):
     """Basic test cases."""
     def setUp(self):
         self.bus = MockSMBus()
         self.sgp=sgp30.sgp30.Sgp30(self.bus)
     def test_read(self):
-        self.sgp.read_measurements()
+        self.assertEqual(self.sgp.read_measurements().data,[400,6])