tests: set NLTST_IN_CI for not skipping tests accidentally

In CI, we know which tests should be skipped. Let github actions set
NLTST_IN_CI=1, and disable certain skip checks.

.github/workflows/ci.yml

@@ -4,6 +4,9 @@ on:
   push:
   pull_request:
 
+env:
+  NLTST_IN_CI: 1
+
 jobs:
   clang-format:
     runs-on: ubuntu-latest

tests/nl-test-util.c

@@ -678,6 +678,13 @@ void _nltst_assert_link_exists_full(const char *ifname, bool exists)
 
 /*****************************************************************************/
 
+bool _nltst_in_ci(void)
+{
+	return _nl_streq0(getenv("NLTST_IN_CI"), "1");
+}
+
+/*****************************************************************************/
+
 bool _nltst_has_iproute2(void)
 {
 	static int has = -1;
@@ -693,6 +700,10 @@ bool _nltst_skip_no_iproute2(const char *msg)
 	if (_nltst_has_iproute2())
 		return false;
 
+	ck_assert_msg(
+		!_nltst_in_ci(),
+		"We seem to not have iproute2, but we are in NLTST_IN_CI=1. This is fatal.");
+
 	printf("skip test due to missing iproute2%s%s%s\n", msg ? " (" : "",
 	       msg ?: "", msg ? ")" : "");
 	return true;

tests/nl-test-util.h

@@ -410,6 +410,8 @@ void nltst_netns_leave(struct nltst_netns *nsdata);
 
 #define _nltst_system(command) _nltst_assert_retcode(system(command))
 
+bool _nltst_in_ci(void);
+
 bool _nltst_has_iproute2(void);
 bool _nltst_skip_no_iproute2(const char *msg);