diff --git a/test/Identity.t.sol b/test/Identity.t.sol
index 5123c90..865ffc1 100644
--- a/test/Identity.t.sol
+++ b/test/Identity.t.sol
@@ -24,6 +24,21 @@ contract IdentityTest is Test {
         assertEq(id.tokenURI(agentId), "ipfs://agent-1");
     }
 
+    function test_agentIdsIncrease() public {
+        address op2 = makeAddr("operator2");
+        vm.prank(operator);
+        uint256 first = id.registerAgent(runtime, "ipfs://agent-1");
+
+        address runtime2 = makeAddr("runtime2");
+        vm.prank(op2);
+        uint256 second = id.registerAgent(runtime2, "ipfs://agent-2");
+
+        assertEq(first, 1);
+        assertEq(second, 2);
+        assertEq(id.ownerOf(first), operator);
+        assertEq(id.ownerOf(second), op2);
+    }
+
     function test_registerAgentEmitsEvent() public {
         vm.expectEmit(true, true, false, true);
         emit IIdentity.AgentRegistered(1, operator, runtime, "ipfs://a");
@@ -45,11 +60,29 @@ contract IdentityTest is Test {
         id.setRuntimeKey(agentId, stranger);
 
         address next = makeAddr("next");
+        vm.expectEmit(true, false, false, true);
+        emit IIdentity.RuntimeKeyChanged(agentId, next);
         vm.prank(operator);
         id.setRuntimeKey(agentId, next);
         assertEq(id.runtimeKeyOf(agentId), next);
     }
 
+    function test_setRuntimeKeyRejectsUnknownAgent() public {
+        address next = makeAddr("next");
+        vm.prank(operator);
+        vm.expectRevert(abi.encodeWithSelector(IIdentity.UnknownAgent.selector, 42));
+        id.setRuntimeKey(42, next);
+    }
+
+    function test_setRuntimeKeyRejectsZeroAddress() public {
+        vm.prank(operator);
+        uint256 agentId = id.registerAgent(runtime, "");
+
+        vm.prank(operator);
+        vm.expectRevert(IIdentity.ZeroRuntimeKey.selector);
+        id.setRuntimeKey(agentId, address(0));
+    }
+
     function test_runtimeKeyFollowsTokenTransferOwnership() public {
         vm.prank(operator);
         uint256 agentId = id.registerAgent(runtime, "");
@@ -57,10 +90,16 @@ contract IdentityTest is Test {
         vm.prank(operator);
         id.transferFrom(operator, buyer, agentId);
         assertEq(id.operatorOf(agentId), buyer);
+        assertEq(id.runtimeKeyOf(agentId), runtime);
     }
 
     function test_unknownAgentReverts() public {
         vm.expectRevert(abi.encodeWithSelector(IIdentity.UnknownAgent.selector, 42));
         id.runtimeKeyOf(42);
     }
+
+    function test_tokenURIOfUnknownAgentReverts() public {
+        vm.expectRevert(abi.encodeWithSelector(IIdentity.UnknownAgent.selector, 42));
+        id.tokenURI(42);
+    }
 }