(5/n) basic margin pool tests (#524)

* (5/n) basic margin pool tests

Author: Sam Barani

packages/margin_trading/tests/margin_pool_math_tests.move

@@ -155,3 +155,35 @@ fun test_borrow_supply(duration: u64, borrow: u64, supply: u64) {
     test::return_shared(pool);
     cleanup_test(registry, admin_cap, maintainer_cap, clock, scenario);
 }
+
+#[test]
+fun test_zero_utilization() {
+    let (mut scenario, mut clock, admin_cap, maintainer_cap, pool_id) = setup_test();
+    scenario.next_tx(test_constants::admin());
+    let mut pool = scenario.take_shared_by_id<MarginPool<USDC>>(pool_id);
+    let registry = scenario.take_shared<MarginRegistry>();
+
+    scenario.next_tx(test_constants::user1());
+    let supply = 100 * test_constants::usdc_multiplier();
+    let coin = mint_coin<USDC>(supply, scenario.ctx());
+    pool.supply(&registry, coin, &clock, scenario.ctx());
+
+    advance_time(&mut clock, margin_constants::year_ms());
+
+    // Withdraw should give back same amount
+    scenario.next_tx(test_constants::user1());
+    let withdrawn_coin = pool.withdraw(&registry, option::none(), &clock, scenario.ctx());
+    assert!(withdrawn_coin.value() == supply);
+    destroy(withdrawn_coin);
+
+    test::return_shared(pool);
+    cleanup_test(registry, admin_cap, maintainer_cap, clock, scenario);
+}
+
+#[test]
+fun test_high_utilization_interest() {
+    let duration = 1;
+    let borrow = 79 * test_constants::usdc_multiplier(); // Just below optimal utilization
+    let supply = 100 * test_constants::usdc_multiplier();
+    test_borrow_supply(duration, borrow, supply);
+}