tests: unittests: add fmt_u64_dec() tests

tests/unittests/tests-fmt/tests-fmt.c

@@ -120,6 +120,42 @@ static void test_fmt_s32_dec(void)
     TEST_ASSERT_EQUAL_STRING("-9876", (char *) out);
 }
 
+static void test_fmt_u64_dec_a(void)
+{
+    char out[21] = "------------------";
+    uint64_t val = 0;
+    uint8_t chars = 0;
+
+    chars = fmt_u64_dec(out, val);
+    TEST_ASSERT_EQUAL_INT(1, chars);
+    out[chars] = '\0';
+    TEST_ASSERT_EQUAL_STRING("0", (char *) out);
+}
+
+static void test_fmt_u64_dec_b(void)
+{
+    char out[21] = "--------------------";
+    uint64_t val = 18446744073709551615LLU;
+    uint8_t chars = 0;
+
+    chars = fmt_u64_dec(out, val);
+    TEST_ASSERT_EQUAL_INT(20, chars);
+    out[chars] = '\0';
+    TEST_ASSERT_EQUAL_STRING("18446744073709551615", (char *) out);
+}
+
+static void test_fmt_u64_dec_c(void)
+{
+    char out[21] = "--------------------";
+    uint64_t val = 1234567890123456789LLU;
+    uint8_t chars = 0;
+
+    chars = fmt_u64_dec(out, val);
+    TEST_ASSERT_EQUAL_INT(19, chars);
+    out[chars] = '\0';
+    TEST_ASSERT_EQUAL_STRING("1234567890123456789", (char *) out);
+}
+
 static void test_rmt_s16_dec(void)
 {
     char out[7] = "-------";
@@ -247,6 +283,9 @@ Test *tests_fmt_tests(void)
         new_TestFixture(test_fmt_u32_hex),
         new_TestFixture(test_fmt_u64_hex),
         new_TestFixture(test_fmt_u32_dec),
+        new_TestFixture(test_fmt_u64_dec_a),
+        new_TestFixture(test_fmt_u64_dec_b),
+        new_TestFixture(test_fmt_u64_dec_c),
         new_TestFixture(test_fmt_u16_dec),
         new_TestFixture(test_fmt_s32_dec),
         new_TestFixture(test_rmt_s16_dec),