stdio: add Linux-specific tests for error checking

tests/hghave.py

@@ -634,3 +634,7 b' def has_zstd():'
         return True
     except ImportError:
         return False
+
+@check("devfull", "/dev/full special file")
+def has_dev_full():
+    return os.path.exists('/dev/full')

tests/test-basic.t

@@ -16,10 +16,31 b' Create a repository:'
   $ hg init t
   $ cd t
 
-Make a changeset:
+Prepare a changeset:
 
   $ echo a > a
   $ hg add a
+
+  $ hg status
+  A a
+
+Writes to stdio succeed and fail appropriately
+
+#if devfull
+  $ hg status 2>/dev/full
+  A a
+
+  $ hg status >/dev/full
+  abort: No space left on device
+  [255]
+
+  $ hg status >/dev/full 2>&1
+  [1]
+
+  $ hg status ENOENT 2>/dev/full
+  [1]
+#endif
+
   $ hg commit -m test
 
 This command is ancient: