tests/unittests: Add tests for endian.h

tests/unittests/tests-libc/tests-libc.c

@@ -8,6 +8,7 @@
 
 #include <stdint.h>
 #include <string.h>
+#include <endian.h>
 #include "string_utils.h"
 
 #include "tests-libc.h"
@@ -39,11 +40,64 @@ static void test_libc_memchk(void)
     TEST_ASSERT(memchk(buffer, 0xff, sizeof(buffer)) == &buffer[5]);
 }
 
+/**
+ * @name    Unit test ensuring `<endian.h>` is provided and correct across
+ *          all platforms
+ * @{
+ */
+union u16 {
+    uint8_t as_bytes[2];
+    uint16_t as_number;
+};
+
+union u32 {
+    uint8_t as_bytes[4];
+    uint32_t as_number;
+};
+
+union u64 {
+    uint8_t as_bytes[8];
+    uint64_t as_number;
+};
+
+static void test_libc_endian(void)
+{
+    /* format the numbers 0x0102, 0x01020304 and 0x0102030405060708
+     * in little/big endian format by hand: */
+    const uint16_t u16_host = 0x0102;
+    const union u16 u16_be = { .as_bytes = { 0x01, 0x02 } };
+    const union u16 u16_le = { .as_bytes = { 0x02, 0x01 } };
+    const uint32_t u32_host = 0x01020304;
+    const union u32 u32_be = { .as_bytes = { 0x01, 0x02, 0x03, 0x04 } };
+    const union u32 u32_le = { .as_bytes = { 0x04, 0x03, 0x02, 0x01 } };
+    const uint64_t u64_host = 0x0102030405060708;
+    const union u64 u64_be = { .as_bytes = { 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08 } };
+    const union u64 u64_le = { .as_bytes = { 0x08, 0x07, 0x06, 0x05, 0x04, 0x03, 0x02, 0x01 } };
+
+    /* check from host to big/little endian */
+    TEST_ASSERT_EQUAL_INT(htobe16(u16_host), u16_be.as_number);
+    TEST_ASSERT_EQUAL_INT(htole16(u16_host), u16_le.as_number);
+    TEST_ASSERT_EQUAL_INT(htobe32(u32_host), u32_be.as_number);
+    TEST_ASSERT_EQUAL_INT(htole32(u32_host), u32_le.as_number);
+    TEST_ASSERT_EQUAL_INT(htobe64(u64_host), u64_be.as_number);
+    TEST_ASSERT_EQUAL_INT(htole64(u64_host), u64_le.as_number);
+
+    /* check little/big endian to host */
+    TEST_ASSERT_EQUAL_INT(be16toh(u16_be.as_number), u16_host);
+    TEST_ASSERT_EQUAL_INT(le16toh(u16_le.as_number), u16_host);
+    TEST_ASSERT_EQUAL_INT(be32toh(u32_be.as_number), u32_host);
+    TEST_ASSERT_EQUAL_INT(le32toh(u32_le.as_number), u32_host);
+    TEST_ASSERT_EQUAL_INT(be64toh(u64_be.as_number), u64_host);
+    TEST_ASSERT_EQUAL_INT(le64toh(u64_le.as_number), u64_host);
+}
+/** @} */
+
 Test *tests_libc_tests(void)
 {
     EMB_UNIT_TESTFIXTURES(fixtures) {
         new_TestFixture(test_libc_strscpy),
         new_TestFixture(test_libc_memchk),
+        new_TestFixture(test_libc_endian),
     };
 
     EMB_UNIT_TESTCALLER(libc_tests, NULL, NULL, fixtures);