text: #include <stan/math/prim.hpp>
  #include <gtest/gtest.h>
  #include <limits>
  
  TEST(MathFunctions, sign) {
    double x;
  
    x = 0;
    EXPECT_EQ(0, stan::math::sign(x));
    x = 0.0000001;
    EXPECT_EQ(1, stan::math::sign(x));
    x = -0.001;
    EXPECT_EQ(-1, stan::math::sign(x));
  }
  
  TEST(MathFunctions, sign_nan) {
    double nan = std::numeric_limits<double>::quiet_NaN();
  
    EXPECT_EQ(1, stan::math::sign(nan));
  }
  