test: test internal borrow caps

Author: AlbertoCentonze

tests/unitary/controller/test_internal_update_total_debt.py

@@ -0,0 +1,47 @@
+# You can access update_total_debt using
+
+import boa
+import pytest
+from textwrap import dedent
+
+from tests.utils.constants import WAD
+
+
+BORROW_CAP = 10**9
+
+
+@pytest.fixture(scope="module", autouse=True)
+def expose_internal(controller):
+    controller.inject_function(
+        dedent("""
+        @external
+        def update_total_debt(d_debt: uint256, rate_mul: uint256, is_increase: bool) -> core.IController.Loan:
+            return core._update_total_debt(d_debt, rate_mul, is_increase)
+        """)
+    )
+
+
+def test_default_behavior(controller):
+    controller.eval("core._total_debt.initial_debt = 0")
+    controller.eval(f"core._total_debt.rate_mul = {WAD}")
+    controller.eval(f"core.borrow_cap = {BORROW_CAP}")
+
+    controller.inject.update_total_debt(BORROW_CAP - 1, WAD, True)
+    current_debt = controller.eval("core._total_debt.initial_debt")
+    assert current_debt == BORROW_CAP - 1
+
+    controller.inject.update_total_debt(1, WAD, True)
+    current_debt = controller.eval("core._total_debt.initial_debt")
+    assert current_debt == BORROW_CAP
+
+
+def test_exceeding_borrow_cap_reverts(controller):
+    controller.eval(f"core._total_debt.rate_mul = {WAD}")
+    controller.eval(f"core.borrow_cap = {BORROW_CAP}")
+    controller.eval(f"core._total_debt.initial_debt = {BORROW_CAP}")
+
+    with boa.reverts("Borrow cap exceeded"):
+        controller.inject.update_total_debt(1, WAD, True)
+
+    current_debt = controller.eval("core._total_debt.initial_debt")
+    assert current_debt == BORROW_CAP