diff --git a/tests/mock_smbus2.py b/tests/mock_smbus2.py
index cb14e80..6be1414 100644
--- a/tests/mock_smbus2.py
+++ b/tests/mock_smbus2.py
@@ -1,18 +1,22 @@
 from smbus2 import i2c_msg
+from collections import namedtuple 
 
 from .context import sgp30
+from time import time
 
+I2CAnswers= namedtuple("I2CAnswers",["answer","min_delay"])
+I2A = I2CAnswers
 def add_crc(l):
     return l + [sgp30.Crc8().hash(l)]
 
 answers = {
-    (0x36, 0x82): add_crc([0,0]) ,#GET_SERIAL
-    (0x20, 0x15): add_crc([0,0]) ,#GET_FEATURES
-    (0x20, 0x03): None ,#IAQ_INIT
-    (0x20, 0x08): [1, 144, 76, 0, 6, 39] ,#IAQ_MEASURE
-    (0x20, 0x32): add_crc([0xD4,0x00]) ,#IAQ_SELFTEST
-    (0x20, 0x15): [133, 152, 85, 138, 32, 202] ,#GET_BASELINE
-    (0x20, 0x1e): None,#SET_BASELINE
+    (0x36, 0x82): I2A(add_crc([0,0]),.4), #GET_SERIAL
+    (0x20, 0x15): I2A(add_crc([0,0]), 1), #GET_FEATURES
+    (0x20, 0x03): I2A(None, 2), #IAQ_INIT
+    (0x20, 0x08): I2A([1, 144, 76, 0, 6, 39], 10), #IAQ_MEASURE
+    (0x20, 0x32): I2A(add_crc([0xD4,0x00]), 200), #IAQ_SELFTEST
+    (0x20, 0x15): I2A([133, 152, 85, 138, 32, 202], 10), #GET_BASELINE
+    (0x20, 0x1e): I2A(None, 10) #SET_BASELINE
 }
 
 class MockSMBus:
@@ -21,9 +25,15 @@ class MockSMBus:
         s.last=None
         s.addr=None
         s._break_crc=break_crc
+        s._deadline=time() 
+
+    def _set_deadline(s, t):
+        s._deadline=time() + t/1000.
 
     def i2c_rdwr(s,*msgs):
         for m in msgs:
+            if time() < s._deadline:
+                raise IOError("To fast buss-access, device not ready")
             if m.flags == 1:
                 s._process_read(m)
             else:
@@ -45,6 +55,8 @@ class MockSMBus:
                 
 
     def _process_write(s,msg):
-        s.status = answers[tuple(msg)[0:2]]
+        a = answers[tuple(msg)[0:2]]
+        s._set_deadline(a.min_delay)
+        s.status = a.answer
         s.last=msg