Added `silent' expectation handler

src/expect-core

@@ -131,3 +131,20 @@ _expect--match()
   [[ "$(cat)" =~ $pat ]]
 }
 
+
+##
+# Expects that both stdin and stderr (if available) are empty
+_expect--silent()
+{
+  local -r stderr="${3:-/dev/null}"
+  shift "$2"
+
+  # we accept no arguments
+  test $# -eq 0 || _bail_clause silent "$*"
+
+  # quick read using builtins; if we find any single byte, then we know that
+  # it is non-empty
+  read -N1 || read -N1 <"$stderr" || return 0
+  return 1
+}
+

test/test-expect-core

@@ -121,3 +121,37 @@ describe match
   end
 end
 
+
+describe silent
+  it succeeds when both stdout and stderr are empty
+    # omitting stderr arg
+    expect _expect--silent 0 2 < <(:)
+      to succeed
+
+    # empty stderr
+    expect _expect--silent 0 3 <(:) < <(:)
+      to succeed
+  end
+
+  it fails when stdout is empty but stderr is not
+  expect _expect--silent 0 3 <( echo ) < <(:)
+      to fail
+  end
+
+  it fails when stderr is empty but stdout is not
+    # omitting stderr arg
+    expect _expect--silent 0 2 <<< ""
+      to fail
+
+    # empty stderr
+    expect _expect--silent 0 3 <(:) <<< ""
+      to fail
+  end
+
+  # no arguments within context of the DSL, that is
+  it accepts no arguments
+  expect _expect--silent 0 2 foo < <(:)
+      to fail
+  end
+end
+