text: #include <stan/math/prim.hpp>
  #include <gtest/gtest.h>
  #include <cmath>
  #include <limits>
  
  TEST(MathFunctions, trigamma) {
    using stan::math::trigamma;
    EXPECT_FLOAT_EQ(102.9757436100834515253246058208, trigamma(-2.1));
    EXPECT_FLOAT_EQ(stan::math::positive_infinity(), trigamma(-2.0));
    EXPECT_FLOAT_EQ(1.0e12, trigamma(0.000001));
    EXPECT_FLOAT_EQ(0.2616741772864245283534239, trigamma(4.3));
    EXPECT_FLOAT_EQ(0.07404026866401033683840011, trigamma(14.0));
  }
  
  TEST(MathFunctions, trigamma_nan) {
    double nan = std::numeric_limits<double>::quiet_NaN();
  
    EXPECT_TRUE(std::isnan(stan::math::trigamma(nan)));
  }
  