Disable tests of /proc/cpuinfo in LXC containers

It seems that we can't access /proc files when running inside such
containers, so don't try to do it.

tests/file/filetest.cpp

@@ -154,7 +154,10 @@ TEST_CASE("wxFile::Special", "[file][linux][special-file]")
 
     wxString s;
     CHECK( fileProc.ReadAll(&s) );
-    CHECK( !s.empty() );
+
+    // /proc files seem to be always empty in LXC containers.
+    if ( !IsRunningInLXC() )
+        CHECK( !s.empty() );
 
     // All files in /sys have the size of one kernel page, even if they don't
     // have that much data in them.

tests/test.cpp

@@ -69,6 +69,10 @@ std::string wxTheCurrentTestClass, wxTheCurrentTestMethod;
 #endif // __WXGTK__
 #endif // wxUSE_GUI
 
+#ifdef __LINUX__
+    #include "wx/filename.h"
+#endif
+
 #include "wx/socket.h"
 #include "wx/evtloop.h"
 
@@ -418,6 +422,17 @@ extern bool IsRunningUnderXVFB()
     return s_isRunningUnderXVFB == 1;
 }
 
+#ifdef __LINUX__
+
+extern bool IsRunningInLXC()
+{
+    // This is simplistic but should work in the normal cases and can always be
+    // made more precise later if necessary.
+    return wxFileName::DirExists("/dev/lxd");
+}
+
+#endif // __LINUX__
+
 #if wxUSE_GUI
 
 bool EnableUITests()

tests/testprec.h

@@ -123,6 +123,10 @@ extern bool IsAutomaticTest();
 
 extern bool IsRunningUnderXVFB();
 
+#ifdef __LINUX__
+extern bool IsRunningInLXC();
+#endif // __LINUX__
+
 // Helper class setting the locale to the given one for its lifetime.
 class LocaleSetter
 {

tests/textfile/textfiletest.cpp

@@ -348,7 +348,11 @@ TEST_CASE("wxTextFile::Special", "[textfile][linux][special-file]")
     {
         wxTextFile f;
         CHECK( f.Open("/proc/cpuinfo") );
-        CHECK( f.GetLineCount() > 1 );
+
+        // /proc files seem to be always empty in LXC containers, so skip this
+        // check there.
+        if ( !IsRunningInLXC() )
+            CHECK( f.GetLineCount() > 1 );
     }
 
     SECTION("/sys")