Only set up LD_PRELOAD for tests that actually need it.

Makefile

@@ -85,8 +85,7 @@ check: $(OBJS) $(CHECK_BINS)
 	r=true ; for bin in $(CHECK_BINS); do $$bin || r=false; done ; $$r
 
 acceptance: build
-	$(MAKE) -C tests/acceptance/ld_preloads all
-	cd tests/acceptance && LD_PRELOADS=$$(echo ld_preloads/*.o) RUBYOPT='-I.' ruby nbd_scenarios -v
+	cd tests/acceptance && RUBYOPT='-I.' ruby nbd_scenarios -v
 
 test: check acceptance
 
@@ -109,8 +108,6 @@ install:
 
 clean:
 	rm -rf build/*
-	$(RM) $(LD_PRELOAD_OBJ)
-
 
 .PHONY: clean objs check_objs all server proxy check_bins check doc build test acceptance
 

tests/acceptance/test_serve_mode.rb

@@ -40,8 +40,15 @@ class TestServeMode < Test::Unit::TestCase
   end
 
   def setup_msync_catcher
+    `make -C ld_preloads/ msync_catcher.o`
+    omit 'LD_PRELOAD library not found' unless
+      File.exist?('ld_preloads/msync_catcher.o')
+
     @msync_catcher = Tempfile.new('msync')
     ENV['MSYNC_CATCHER_OUTPUT'] = @msync_catcher.path
+
+    @ld_preload_orig = ENV['LD_PRELOAD']
+    ENV['LD_PRELOAD'] = 'ld_preloads/msync_catcher.o'
   end
 
   def parse_msync_output
@@ -56,7 +63,9 @@ class TestServeMode < Test::Unit::TestCase
 
   def teardown_msync_catcher
     @msync_catcher.close if @msync_catcher
+
     ENV.delete 'MSYNC_CATCHER_OUTPUT'
+    ENV['LD_PRELOAD'] = @ld_preload_orig
   end
 
   def test_bad_request_magic_receives_error_response