This is xnu-8019. See this file in:
#include <darwintest.h>
#include <mach/mach.h>
#include <mach/task.h>
#include <mach/mach_init.h>

T_GLOBAL_META(
	T_META_NAMESPACE("xnu.ipc"),
	T_META_RUN_CONCURRENTLY(TRUE),
	T_META_RADAR_COMPONENT_NAME("xnu"),
	T_META_RADAR_COMPONENT_VERSION("IPC"));

T_DECL(mach_task_is_self,
    "test task port comparison check")
{
	mach_port_t self_insp, self_read, self_name, port;

	T_ASSERT_MACH_SUCCESS(task_get_special_port(mach_task_self(), TASK_READ_PORT, &self_read), "task_get_special_port failed");
	T_ASSERT_MACH_SUCCESS(task_get_special_port(mach_task_self(), TASK_INSPECT_PORT, &self_insp), "task_get_special_port failed");
	T_ASSERT_MACH_SUCCESS(task_get_special_port(mach_task_self(), TASK_NAME_PORT, &self_name), "task_get_special_port failed");

	T_ASSERT_MACH_SUCCESS(mach_port_allocate(mach_task_self(), MACH_PORT_RIGHT_RECEIVE, &port), "mach_port_allocate failed");

	T_EXPECT_NE(self_read, self_insp, "read and inspect port should be different");
	T_EXPECT_NE(self_read, mach_task_self(), "read and control port should be different");

	T_EXPECT_EQ(1, mach_task_is_self(mach_task_self()), "control port should point to self");
	T_EXPECT_EQ(1, mach_task_is_self(self_read), "read port should point to self");
	T_EXPECT_EQ(1, mach_task_is_self(self_insp), "inspect port should point to self");
	T_EXPECT_EQ(1, mach_task_is_self(self_name), "name port should point to self");
	T_EXPECT_NE(1, mach_task_is_self(port), "_port_ should not point to self");
}