test: minor modernization

Coverity was complaining that read() does not terminate the data. But
we did that termination earlier, so covirity is wrong (CID#1402306, CID#1402340).
Let's modernize the style a bit nevertheless.

(size_t) cast is needed to avoid the warning about comparison, iff
the value is not a constant.

src/test/test-copy.c

@@ -52,8 +52,8 @@ static void test_copy_file_fd(void) {
         char in_fn[] = "/tmp/test-copy-file-fd-XXXXXX";
         char out_fn[] = "/tmp/test-copy-file-fd-XXXXXX";
         _cleanup_close_ int in_fd = -1, out_fd = -1;
-        char text[] = "boohoo\nfoo\n\tbar\n";
-        char buf[64] = {0};
+        const char *text = "boohoo\nfoo\n\tbar\n";
+        char buf[64] = {};
 
         log_info("%s", __func__);
 
@@ -67,7 +67,7 @@ static void test_copy_file_fd(void) {
         assert_se(copy_file_fd(in_fn, out_fd, COPY_REFLINK) >= 0);
         assert_se(lseek(out_fd, SEEK_SET, 0) == 0);
 
-        assert_se(read(out_fd, buf, sizeof(buf)) == sizeof(text) - 1);
+        assert_se(read(out_fd, buf, sizeof buf) == (ssize_t) strlen(text));
         assert_se(streq(buf, text));
 
         unlink(in_fn);

src/test/test-fileio.c

@@ -427,7 +427,7 @@ static void test_write_string_file(void) {
 static void test_write_string_file_no_create(void) {
         _cleanup_(unlink_tempfilep) char fn[] = "/tmp/test-write_string_file_no_create-XXXXXX";
         _cleanup_close_ int fd;
-        char buf[64] = {0};
+        char buf[64] = {};
 
         fd = mkostemp_safe(fn);
         assert_se(fd >= 0);
@@ -435,7 +435,7 @@ static void test_write_string_file_no_create(void) {
         assert_se(write_string_file("/a/file/which/does/not/exists/i/guess", "boohoo", 0) < 0);
         assert_se(write_string_file(fn, "boohoo", 0) == 0);
 
-        assert_se(read(fd, buf, sizeof(buf)) == STRLEN("boohoo\n"));
+        assert_se(read(fd, buf, sizeof buf) == (ssize_t) strlen("boohoo\n"));
         assert_se(streq(buf, "boohoo\n"));
 }