added iif and tif functions

app/lib/irt/test_information_function.py

@@ -0,0 +1,16 @@
+from lib.irt.item_information_function import ItemInformationFunction
+
+class TestInformationFunction():
+  def __init__(self, irt_model):
+    self.irt_model = irt_model
+    self.iif = ItemInformationFunction(irt_model)
+
+  def calculate(self, items, **kwargs):
+    sum = 0
+
+    for item in items:
+      result = self.iif.calculate(b_param=item.b_param, theta=kwargs['theta'])
+      item.iif = result
+      sum += item.iif
+
+    return sum