fixed interaction vertices test.

  dca::phys::solver::ctint::InteractionVertices H;

  using Element = dca::phys::solver::ctint::InteractionElement;

  H.insertElement(Element{{0, 0, 0, 0}, {0, 1, 2, 3}, 1.});  // pair-hop 1

  H.insertElement(Element{{0, 0, 0, 0}, {0, 0, 2, 2}, 1.});  // density-density

  H.insertElement(Element{{0, 0, 0, 0}, {1, 0, 3, 2}, 1.});  // pair-hop 2

  auto el1 = Element{{0, 0, 0, 0}, {0, 1, 2, 3}, 1.};  // pair-hop 1

  auto el2 = Element{{0, 0, 0, 0}, {0, 0, 2, 2}, 1.};  // density-density

  auto el3 = Element{{0, 0, 0, 0}, {1, 0, 3, 2}, 1.};  // pair-hop 2

  // Partners only on the same site

  H.initialize(1, false);

  for (auto el : {el1, el2, el3})

    H.insertElement(el);

  EXPECT_EQ(std::vector<ushort>{2}, H[0].partners_id);

  EXPECT_EQ(std::vector<ushort>{}, H[1].partners_id);

  EXPECT_EQ(std::vector<ushort>{0}, H[2].partners_id);

  // No double insertion.

  H.reset();

  H.initialize(0, false);

  for (auto el : {el1, el2, el3})

    H.insertElement(el);

  for (int i = 0; i < 3; ++i)

    EXPECT_EQ(std::vector<ushort>{}, H[i].partners_id);

}

TEST(InteractionVerticesTest, SamplingProb) {