From 585d317947455f06aa951e5d8f8fc626d2fc6b39 Mon Sep 17 00:00:00 2001
From: jzmaddock <john@johnmaddock.co.uk>
Date: Wed, 18 Feb 2026 16:35:23 +0000
Subject: [PATCH] NC T finders: Improve code coverage.

---
 include/boost/math/distributions/non_central_t.hpp | 2 +-
 test/test_nc_t.hpp                                 | 7 +++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/include/boost/math/distributions/non_central_t.hpp b/include/boost/math/distributions/non_central_t.hpp
index c0c898387..9bc1cf8cc 100644
--- a/include/boost/math/distributions/non_central_t.hpp
+++ b/include/boost/math/distributions/non_central_t.hpp
@@ -751,7 +751,7 @@ namespace boost
                //
                // Can't find a thing if one of p and q is zero:
                //
-               return policies::raise_evaluation_error<RealType>(function, "Can't find degrees of freedom when the probability is 0 or 1, only possible answer is %1%", // LCOV_EXCL_LINE
+               return policies::raise_evaluation_error<RealType>(function, "Can't find degrees of freedom when the probability is 0 or 1, only possible answer is %1%",
                   RealType(std::numeric_limits<RealType>::quiet_NaN()), Policy()); // LCOV_EXCL_LINE
             }
             if (fabs(x) < tools::epsilon<RealType>())
diff --git a/test/test_nc_t.hpp b/test/test_nc_t.hpp
index 58a48511d..83dbf12c9 100644
--- a/test/test_nc_t.hpp
+++ b/test/test_nc_t.hpp
@@ -541,6 +541,13 @@ void quantile_sanity_check(T& data, const char* type_name, const char* test)
          {
             BOOST_ERROR(e.what());
          }
+         // Code coverage:
+         BOOST_CHECK_THROW(boost::math::non_central_t_distribution<value_type>::find_degrees_of_freedom(data[i][1], boost::math::tools::epsilon<value_type>() / 2, data[i][3]), boost::math::evaluation_error);
+         BOOST_CHECK_THROW(boost::math::non_central_t_distribution<value_type>::find_degrees_of_freedom(boost::math::complement(data[i][1], boost::math::tools::epsilon<value_type>() / 2, data[i][3])), boost::math::evaluation_error);
+         BOOST_CHECK_THROW(boost::math::non_central_t_distribution<value_type>::find_degrees_of_freedom(data[i][1], data[i][2], value_type(0)), boost::math::evaluation_error);
+         BOOST_CHECK_THROW(boost::math::non_central_t_distribution<value_type>::find_degrees_of_freedom(boost::math::complement(data[i][1], data[i][2], value_type(0))), boost::math::evaluation_error);
+         BOOST_CHECK_THROW(boost::math::non_central_t_distribution<value_type>::find_degrees_of_freedom(data[i][1], data[i][2], value_type(1)), boost::math::evaluation_error);
+         BOOST_CHECK_THROW(boost::math::non_central_t_distribution<value_type>::find_degrees_of_freedom(boost::math::complement(data[i][1], data[i][2], value_type(1))), boost::math::evaluation_error);
       }
    }
 #endif