Example of updating to api test case with closure/func annotation for post-upgrade assertion

TestAgentService_Register_MeshGateway.patch

diff --git a/api/agent_test.go b/api/agent_test.go
index ebf7381547..bfe27325c1 100644
--- a/api/agent_test.go
+++ b/api/agent_test.go
@@ -1927,28 +1927,33 @@ func TestAgentService_Register_MeshGateway(t *testing.T) {
 
 	agent := c.Agent()
 
-	reg := AgentServiceRegistration{
-		Kind:    ServiceKindMeshGateway,
-		Name:    "mesh-gateway",
-		Address: "10.1.2.3",
-		Port:    8443,
-		Proxy: &AgentServiceConnectProxyConfig{
-			Config: map[string]interface{}{
-				"foo": "bar",
+	// +upgrade-test-generator:assertion
+	doAssertion := func(c *Client, t *testing.T) {
+		reg := AgentServiceRegistration{
+			Kind:    ServiceKindMeshGateway,
+			Name:    "mesh-gateway",
+			Address: "10.1.2.3",
+			Port:    8443,
+			Proxy: &AgentServiceConnectProxyConfig{
+				Config: map[string]interface{}{
+					"foo": "bar",
+				},
 			},
-		},
-	}
+		}
 
-	err := agent.ServiceRegister(&reg)
-	require.NoError(t, err)
+		err := agent.ServiceRegister(&reg)
+		require.NoError(t, err)
 
-	svc, _, err := agent.Service("mesh-gateway", nil)
-	require.NoError(t, err)
-	require.NotNil(t, svc)
-	require.Equal(t, ServiceKindMeshGateway, svc.Kind)
-	require.NotNil(t, svc.Proxy)
-	require.Contains(t, svc.Proxy.Config, "foo")
-	require.Equal(t, "bar", svc.Proxy.Config["foo"])
+		svc, _, err := agent.Service("mesh-gateway", nil)
+		require.NoError(t, err)
+		require.NotNil(t, svc)
+		require.Equal(t, ServiceKindMeshGateway, svc.Kind)
+		require.NotNil(t, svc.Proxy)
+		require.Contains(t, svc.Proxy.Config, "foo")
+		require.Equal(t, "bar", svc.Proxy.Config["foo"])
+	}
+
+	doAssertion(c, t)
 }
 
 func TestAgentService_Register_TerminatingGateway(t *testing.T) {