message: Add more case for WPO's get_num_outer_preds tests
  Summary: The fix for WPO added thorough tests cases already, so just add another case to test content of get_num_outer_preds and add comment for test referring the fix.
diff: @@ -858,6 +858,10 @@ TEST(WeakPartialOrderingTest, exampleFromWpoPaperIrreducible) {
  }
  }
  +/*
  + * Test case of get_num_outer_preds issue that
  + * https://github.com/facebookincubator/SPARTA/pull/7 fixed.
  + */
  TEST(WeakPartialOrderingTest, handlingOuterPreds) {
  {
  SimpleGraph2 g;
  @@ -947,6 +951,24 @@ TEST(WeakPartialOrderingTest, handlingOuterPreds) {
  EXPECT_EQ(wpo.get_node(wpo.get_head_of_exit(v)), wpo.get_node(v))
  << wpo.get_node(v);
  wto << ')';
  +
  + if (wpo.get_node(v) == "46") {
  + // get_num_outer_preds of exit node "46" should return two pair,
  + // one is head node "46" and number 2, another pair is node "74"
  + // and number 1.
  + int count_preds = 0;
  + for (auto pred_pair : wpo.get_num_outer_preds(v)) {
  + if (pred_pair.second == 1) {
  + ++count_preds;
  + EXPECT_EQ(wpo.get_node(pred_pair.first), "74");
  + }
  + if (pred_pair.second == 2) {
  + ++count_preds;
  + EXPECT_EQ(wpo.get_node(pred_pair.first), "46");
  + }
  + }
  + EXPECT_EQ(count_preds, 2);
  + }
  } else {
  if (!first) {
  wto << ' ';
  