diff --git a/test/PurchaseToken.t.sol b/test/PurchaseToken.t.sol
index 363c955..01d76ca 100644
--- a/test/PurchaseToken.t.sol
+++ b/test/PurchaseToken.t.sol
@@ -30,10 +30,22 @@ contract PurchaseTokenTest is Test {
         assertEq(token.symbol(), "PT");
     }
 
+    function testAllowance() public {
+        assertEq(token.allowance(alice, bob), 0);
+    }
+
+    function testBalanceOf() public {
+        assertEq(token.balanceOf(alice), 0);
+    }
+
     function testDecimals() public {
         assertEq(token.decimals(), 18);
     }
 
+    function testTotalSupply() public {
+        assertEq(token.totalSupply(), 0);
+    }
+
     function testMint() public {
         vm.deal(alice, 1 ether);
         assertEq(token.balanceOf(alice), 0);
@@ -46,6 +58,12 @@ contract PurchaseTokenTest is Test {
         assertEq(token.totalSupply(), 1e19);
     }
 
+    function testMintInvalid() public {
+        vm.prank(address(0));
+        vm.expectRevert("ERC20: mint to the zero address");
+        token.mint();
+    }
+
     function testMintInsufficientFunds() public {
         vm.deal(alice, 0.01 ether);
         assertEq(token.balanceOf(alice), 0);