tests/ztest/fail: Replace native_posix with native_sim

In the docs replace references to native_posix with native_sim
Switch the default test platform to native_sim from native_posix

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>

doc/develop/test/ztest.rst

@@ -340,6 +340,8 @@ it needs to report either a pass or fail.  For example:
 
    ZTEST_SUITE(common, NULL, NULL, NULL, NULL, NULL);
 
+.. _ztest_unit_testing:
+
 Quick start - Unit testing
 **************************
 

tests/ztest/fail/README.rst

@@ -7,8 +7,9 @@ Overview
 ********
 
 In order to test the actual framework's failure cases, this test suite has to do something unique.
-There's a subdirectory to this test called 'core'. This project builds a sample ``native_posix`` or
+There's a subdirectory to this test called 'core'. This project builds a sample as a
-``unit_testing`` binary which is expected to fail by calling one of the following:
+:ref:`native_sim <native_sim>` or `:ref:unit_testing <ztest_unit_testing>`
+binary which is expected to fail by calling one of the following:
 - ``ztest_test_fail()`` during either the ``after`` or ``teardown`` phase of the test suite
 - ``ztest_test_skip()`` during either the ``after`` or ``teardown`` phase of the test suite
 - ``ztest_test_pass()`` during either the ``after`` or ``teardown`` phase of the test suite

tests/ztest/fail/testcase.yaml

@@ -5,7 +5,12 @@ common:
   tags:
     - test_framework
   # test has dependencies on host libc
-  platform_allow: native_posix
+  platform_allow:
+    - native_posix
+    - native_sim
+    - native_sim_64
+  integration_platforms:
+    - native_sim
 tests:
   testing.fail.unit.assert_after:
     extra_configs: