test: fix use of ERRNO_IS_PRIVILEGE()

Given that ERRNO_IS_PRIVILEGE() also matches positive values,
make sure this macro is not called with arguments that do not have
errno semantics.

In this case the arguments passed to ERRNO_IS_PRIVILEGE() are the values
returned by read_one_line_file() which can legitimately return positive
values without errno semantics, so fix this by moving ERRNO_IS_PRIVILEGE()
invocations to the branches where the return values are known to be negative.

src/test/test-capability.c

@@ -39,7 +39,7 @@ static void test_last_cap_file(void) {
         int r;
 
         r = read_one_line_file("/proc/sys/kernel/cap_last_cap", &content);
-        if (r == -ENOENT || ERRNO_IS_PRIVILEGE(r)) /* kernel pre 3.2 or no access */
+        if (r == -ENOENT || (r < 0 && ERRNO_IS_PRIVILEGE(r))) /* kernel pre 3.2 or no access */
                 return;
         assert_se(r >= 0);
 
@@ -235,7 +235,7 @@ static void test_ensure_cap_64_bit(void) {
         int r;
 
         r = read_one_line_file("/proc/sys/kernel/cap_last_cap", &content);
-        if (r == -ENOENT || ERRNO_IS_PRIVILEGE(r)) /* kernel pre 3.2 or no access */
+        if (r == -ENOENT || (r < 0 && ERRNO_IS_PRIVILEGE(r))) /* kernel pre 3.2 or no access */
                 return;
         assert_se(r >= 0);
 

src/test/test-fileio.c

@@ -490,7 +490,7 @@ TEST(write_string_file_verify) {
         int r;
 
         r = read_one_line_file("/proc/version", &buf);
-        if (ERRNO_IS_PRIVILEGE(r))
+        if (r < 0 && ERRNO_IS_PRIVILEGE(r))
                 return;
         assert_se(r >= 0);
         assert_se(buf2 = strjoin(buf, "\n"));