Add a test to check that not more compositions than max_compositions is requested (#21)

* Add a test to check we don't allow more compositions than
max_compositions

* Fix typo in calling compositions

Co-authored-by: Lukas Wutschitz <lukas.wutschitz@microsoft.com>

prv_accountant/accountant.py

@@ -96,5 +96,5 @@ class Accountant:
                                            approximation of true epsilon,
                                            upper bound of true epsilon
         """
-        f_n = self.composer.compute_composition(num_compositions=num_compositions)
+        f_n = self.compute_compositions(num_compositions=num_compositions)
         return f_n.compute_epsilon(self.delta, self.delta_error, self.eps_error)

tests/test_accountant.py

@@ -31,6 +31,18 @@ class TestAccountant:
         assert delta_upper == pytest.approx(delta_exact, rel=1e-3)
         assert delta_lower == pytest.approx(delta_exact, rel=1e-3)
 
+    def test_throw_exceeding_max_compositions(self):
+        with pytest.raises(ValueError):
+            accountant = Accountant(
+                noise_multiplier=100.0,
+                sampling_probability=1.0,
+                delta=1e-8,
+                eps_error=0.01,
+                max_compositions=10000
+            )
+
+            accountant.compute_compositions(10001)
+
     def test_throw_error_small_delta(self):
         with pytest.raises(ValueError):
             accountant = Accountant(