review: add test for invalid format err

Author: inbelic

llvm/test/tools/llvm-objcopy/DXContainer/extract-section-errs.test

@@ -19,3 +19,22 @@ Parts:
   - Name:            FKE0
     Size:            8
 ...
+
+## We can't extract a part that is specified incorrectly.
+# RUN: yaml2obj %s --docnum=2 -o %t2
+# RUN: not llvm-objcopy %t2 --extract-section=FKE0,%t.fke0.out 2>&1 | FileCheck %s -DFILE=%t2 --check-prefix=ERROR2
+
+# ERROR2: error: bad format for --extract-section, expected section=file
+
+--- !dxcontainer
+Header:
+  Hash:            [ 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
+                     0x0, 0x0, 0x0, 0x0, 0x0, 0x0 ]
+  Version:
+    Major:           1
+    Minor:           0
+  PartCount:       1
+Parts:
+  - Name:            FKE0
+    Size:            8
+...