tests: lib: time: add test for time() function

Add test cases for time() function.

Signed-off-by: Marcin Niestroj <m.niestroj@emb.dev>

tests/lib/time/CMakeLists.txt

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+# SPDX-License-Identifier: Apache-2.0
+
+cmake_minimum_required(VERSION 3.13.1)
+find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
+project(time)
+
+FILE(GLOB app_sources src/*.c)
+target_sources(app PRIVATE ${app_sources})

tests/lib/time/prj.conf

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+CONFIG_ZTEST=y
+CONFIG_POSIX_CLOCK=y

tests/lib/time/src/main.c

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+/*
+ * Copyright (c) 2021 Golioth, Inc.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <ztest.h>
+#include <time.h>
+
+static void test_time_passing(void)
+{
+	time_t time_initial_unaligned;
+	time_t time_initial;
+	time_t time_current;
+	int i;
+
+	time_initial_unaligned = time(NULL);
+	zassert_true(time_initial_unaligned >= 0, "Fail to get time");
+
+	/* Wait until time() will return new value, which should be aligned */
+	for (i = 0; i < 100; i++) {
+		k_sleep(K_MSEC(10));
+
+		if (time(NULL) != time_initial_unaligned) {
+			break;
+		}
+	}
+
+	time_initial = time(NULL);
+	zassert_equal(time_initial, time_initial_unaligned + 1,
+		      "Time (%d) should be one second larger than initially (%d)",
+		      time_initial, time_initial_unaligned);
+
+	for (i = 1; i <= 10; i++) {
+		k_sleep(K_SECONDS(1));
+
+		time_current = time(NULL);
+		zassert_equal(time_current, time_initial + i,
+			      "Current time (%d) does not match expected time (%d)",
+			      (int) time_current, (int) (time_initial + i));
+	}
+}
+
+static void test_time_param(void)
+{
+	time_t time_result;
+	time_t time_param;
+	int i;
+
+	time_result = time(&time_param);
+
+	zassert_equal(time_result, time_param,
+		      "time() result does not match param value");
+
+	for (i = 0; i < 10; i++) {
+		k_sleep(K_SECONDS(1));
+
+		zassert_equal(time_result, time_param,
+		      "time() result does not match param value");
+	}
+}
+
+void test_main(void)
+{
+	ztest_test_suite(libc_time,
+			ztest_unit_test(test_time_passing),
+			ztest_unit_test(test_time_param)
+			);
+	ztest_run_test_suite(libc_time);
+}

tests/lib/time/testcase.yaml

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+tests:
+  libraries.libc.time:
+    tags: libc
+    filter: not CONFIG_ARCH_POSIX or CONFIG_NATIVE_POSIX_SLOWDOWN_TO_REAL_TIME
+    integration_platforms:
+      - mps2_an385