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diff --git a/tests/SelfTest/UsageTests/Approx.tests.cpp b/tests/SelfTest/UsageTests/Approx.tests.cpp
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+
+//              Copyright Catch2 Authors
+// Distributed under the Boost Software License, Version 1.0.
+//   (See accompanying file LICENSE.txt or copy at
+//        https://www.boost.org/LICENSE_1_0.txt)
+
+// SPDX-License-Identifier: BSL-1.0
+
+#include <catch2/catch_test_macros.hpp>
+#include <catch2/catch_approx.hpp>
+
+#include <cmath>
+
+using Catch::Approx;
+
+namespace {
+    static double divide(double a, double b) {
+        return a / b;
+    }
+
+    class StrongDoubleTypedef {
+        double d_ = 0.0;
+
+    public:
+        explicit StrongDoubleTypedef(double d) : d_(d) {}
+        explicit operator double() const { return d_; }
+    };
+
+    static std::ostream& operator<<(std::ostream& os, StrongDoubleTypedef td) {
+        return os << "StrongDoubleTypedef(" << static_cast<double>(td) << ")";
+    }
+} // end unnamed namespace
+
+using namespace Catch::literals;
+
+///////////////////////////////////////////////////////////////////////////////
+TEST_CASE( "A comparison that uses literals instead of the normal constructor", "[Approx]" ) {
+    double d = 1.23;
+
+    REQUIRE( d == 1.23_a );
+    REQUIRE( d != 1.22_a );
+    REQUIRE( -d == -1.23_a );
+
+    REQUIRE( d == 1.2_a .epsilon(.1) );
+    REQUIRE( d != 1.2_a .epsilon(.001) );
+    REQUIRE( d == 1_a .epsilon(.3) );
+}
+
+TEST_CASE( "Some simple comparisons between doubles", "[Approx]" ) {
+    double d = 1.23;
+
+    REQUIRE( d == Approx( 1.23 ) );
+    REQUIRE( d != Approx( 1.22 ) );
+    REQUIRE( d != Approx( 1.24 ) );
+
+    REQUIRE( d == 1.23_a );
+    REQUIRE( d != 1.22_a );
+
+    REQUIRE( Approx( d ) == 1.23 );
+    REQUIRE( Approx( d ) != 1.22 );
+    REQUIRE( Approx( d ) != 1.24 );
+}
+
+///////////////////////////////////////////////////////////////////////////////
+TEST_CASE( "Approximate comparisons with different epsilons", "[Approx]" ) {
+    double d = 1.23;
+
+    REQUIRE( d != Approx( 1.231 ) );
+    REQUIRE( d == Approx( 1.231 ).epsilon( 0.1 ) );
+}
+
+///////////////////////////////////////////////////////////////////////////////
+TEST_CASE( "Less-than inequalities with different epsilons", "[Approx]" ) {
+  double d = 1.23;
+
+  REQUIRE( d <= Approx( 1.24 ) );
+  REQUIRE( d <= Approx( 1.23 ) );
+  REQUIRE_FALSE( d <= Approx( 1.22 ) );
+  REQUIRE( d <= Approx( 1.22 ).epsilon(0.1) );
+}
+
+///////////////////////////////////////////////////////////////////////////////
+TEST_CASE( "Greater-than inequalities with different epsilons", "[Approx]" ) {
+  double d = 1.23;
+
+  REQUIRE( d >= Approx( 1.22 ) );
+  REQUIRE( d >= Approx( 1.23 ) );
+  REQUIRE_FALSE( d >= Approx( 1.24 ) );
+  REQUIRE( d >= Approx( 1.24 ).epsilon(0.1) );
+}
+
+///////////////////////////////////////////////////////////////////////////////
+TEST_CASE( "Approximate comparisons with floats", "[Approx]" ) {
+    REQUIRE( 1.23f == Approx( 1.23f ) );
+    REQUIRE( 0.0f == Approx( 0.0f ) );
+}
+
+///////////////////////////////////////////////////////////////////////////////
+TEST_CASE( "Approximate comparisons with ints", "[Approx]" ) {
+    REQUIRE( 1 == Approx( 1 ) );
+    REQUIRE( 0 == Approx( 0 ) );
+}
+
+///////////////////////////////////////////////////////////////////////////////
+TEST_CASE( "Approximate comparisons with mixed numeric types", "[Approx]" ) {
+    const double dZero = 0;
+    const double dSmall = 0.00001;
+    const double dMedium = 1.234;
+
+    REQUIRE( 1.0f == Approx( 1 ) );
+    REQUIRE( 0 == Approx( dZero) );
+    REQUIRE( 0 == Approx( dSmall ).margin( 0.001 ) );
+    REQUIRE( 1.234f == Approx( dMedium ) );
+    REQUIRE( dMedium == Approx( 1.234f ) );
+}
+
+///////////////////////////////////////////////////////////////////////////////
+TEST_CASE( "Use a custom approx", "[Approx][custom]" ) {
+    double d = 1.23;
+
+    Approx approx = Approx::custom().epsilon( 0.01 );
+
+    REQUIRE( d == approx( 1.23 ) );
+    REQUIRE( d == approx( 1.22 ) );
+    REQUIRE( d == approx( 1.24 ) );
+    REQUIRE( d != approx( 1.25 ) );
+
+    REQUIRE( approx( d ) == 1.23 );
+    REQUIRE( approx( d ) == 1.22 );
+    REQUIRE( approx( d ) == 1.24 );
+    REQUIRE( approx( d ) != 1.25 );
+}
+
+TEST_CASE( "Approximate PI", "[Approx][PI]" ) {
+    REQUIRE( divide( 22, 7 ) == Approx( 3.141 ).epsilon( 0.001 ) );
+    REQUIRE( divide( 22, 7 ) != Approx( 3.141 ).epsilon( 0.0001 ) );
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+TEST_CASE( "Absolute margin", "[Approx]" ) {
+    REQUIRE( 104.0 != Approx(100.0) );
+    REQUIRE( 104.0 == Approx(100.0).margin(5) );
+    REQUIRE( 104.0 == Approx(100.0).margin(4) );
+    REQUIRE( 104.0 != Approx(100.0).margin(3) );
+    REQUIRE( 100.3 != Approx(100.0) );
+    REQUIRE( 100.3 == Approx(100.0).margin(0.5) );
+}
+
+TEST_CASE("Approx with exactly-representable margin", "[Approx]") {
+    CHECK( 0.25f == Approx(0.0f).margin(0.25f) );
+
+    CHECK( 0.0f == Approx(0.25f).margin(0.25f) );
+    CHECK( 0.5f == Approx(0.25f).margin(0.25f) );
+
+    CHECK( 245.0f == Approx(245.25f).margin(0.25f) );
+    CHECK( 245.5f == Approx(245.25f).margin(0.25f) );
+}
+
+TEST_CASE("Approx setters validate their arguments", "[Approx]") {
+    REQUIRE_NOTHROW(Approx(0).margin(0));
+    REQUIRE_NOTHROW(Approx(0).margin(1234656));
+
+    REQUIRE_THROWS_AS(Approx(0).margin(-2), std::domain_error);
+
+    REQUIRE_NOTHROW(Approx(0).epsilon(0));
+    REQUIRE_NOTHROW(Approx(0).epsilon(1));
+
+    REQUIRE_THROWS_AS(Approx(0).epsilon(-0.001), std::domain_error);
+    REQUIRE_THROWS_AS(Approx(0).epsilon(1.0001), std::domain_error);
+}
+
+TEST_CASE("Default scale is invisible to comparison", "[Approx]") {
+    REQUIRE(101.000001 != Approx(100).epsilon(0.01));
+    REQUIRE(std::pow(10, -5) != Approx(std::pow(10, -7)));
+}
+
+TEST_CASE("Epsilon only applies to Approx's value", "[Approx]") {
+    REQUIRE(101.01 != Approx(100).epsilon(0.01));
+}
+
+TEST_CASE("Assorted miscellaneous tests", "[Approx][approvals]") {
+    REQUIRE(INFINITY == Approx(INFINITY));
+    REQUIRE(-INFINITY != Approx(INFINITY));
+    REQUIRE(1 != Approx(INFINITY));
+    REQUIRE(INFINITY != Approx(1));
+    REQUIRE(NAN != Approx(NAN));
+    REQUIRE_FALSE(NAN == Approx(NAN));
+}
+
+TEST_CASE( "Comparison with explicitly convertible types", "[Approx]" )
+{
+  StrongDoubleTypedef td(10.0);
+
+  REQUIRE(td == Approx(10.0));
+  REQUIRE(Approx(10.0) == td);
+
+  REQUIRE(td != Approx(11.0));
+  REQUIRE(Approx(11.0) != td);
+
+  REQUIRE(td <= Approx(10.0));
+  REQUIRE(td <= Approx(11.0));
+  REQUIRE(Approx(10.0) <= td);
+  REQUIRE(Approx(9.0) <= td);
+
+  REQUIRE(td >= Approx(9.0));
+  REQUIRE(td >= Approx(td));
+  REQUIRE(Approx(td) >= td);
+  REQUIRE(Approx(11.0) >= td);
+
+}
+
+TEST_CASE("Approx::operator() is const correct", "[Approx][.approvals]") {
+    const Approx ap = Approx(0.0).margin(0.01);
+
+    // As long as this compiles, the test should be considered passing
+    REQUIRE(1.0 == ap(1.0));
+}