diff --git a/test/unit_test/runtime/almost_equals.h b/test/unit_test/runtime/almost_equals.h
new file mode 100644
index 00000000..f8362143
--- /dev/null
+++ b/test/unit_test/runtime/almost_equals.h
@@ -0,0 +1,56 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2018 Mateusz Pusz
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#include <catch2/matchers/catch_matchers_templated.hpp>
+#include <units/format.h>
+#include <units/quantity.h>
+
+namespace units {
+
+template<Quantity T>
+struct AlmostEqualsMatcher : Catch::Matchers::MatcherGenericBase {
+  AlmostEqualsMatcher(const T& target) : target_{target} {}
+
+  template<Quantity U>
+    requires std::three_way_comparable_with<T, U> && std::same_as<typename T::rep, typename U::rep> &&
+             treat_as_floating_point<typename T::rep> bool
+  match(const U& other) const
+  {
+    using common = std::common_type_t<T, U>;
+    auto maxTUOne =
+      std::max({typename T::rep(1), std::abs(common(target_).number()), std::abs(common(other).number())});
+    return abs(target_ - other).number() <= std::numeric_limits<typename T::rep>::epsilon() * maxTUOne;
+  }
+
+  std::string describe() const override { return "almost equals: " + STD_FMT::format("{}", target_); }
+
+private:
+  const T& target_;
+};
+
+template<Quantity T>
+AlmostEqualsMatcher<T> AlmostEquals(const T& target)
+{
+  return {target};
+}
+
+}  // namespace units
diff --git a/test/unit_test/runtime/math_test.cpp b/test/unit_test/runtime/math_test.cpp
index dc73da88..91b8ef82 100644
--- a/test/unit_test/runtime/math_test.cpp
+++ b/test/unit_test/runtime/math_test.cpp
@@ -20,6 +20,7 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#include "almost_equals.h"
 #include <catch2/catch_all.hpp>
 #include <units/isq/si/area.h>
 #include <units/isq/si/cgs/length.h>
@@ -386,3 +387,73 @@ TEST_CASE("hypot functions", "[hypot]")
     REQUIRE(hypot(km<>(2.), cgs::length::cm<>(300'000.), km<>(6.)) == km<>(7.));
   }
 }
+
+TEST_CASE("trigonometric functions", "[trig]")
+{
+  using namespace units::aliases;
+
+  SECTION("sin")
+  {
+    REQUIRE_THAT(sin(deg<>(0.)), AlmostEquals(quantity{0.}));
+    REQUIRE_THAT(sin(deg<>(90.)), AlmostEquals(quantity{1.}));
+    REQUIRE_THAT(sin(deg<>(180.)), AlmostEquals(quantity{0.}));
+    REQUIRE_THAT(sin(deg<>(270.)), AlmostEquals(quantity{-1.}));
+
+    REQUIRE_THAT(sin(grad<>(0.)), AlmostEquals(quantity{0.}));
+    REQUIRE_THAT(sin(grad<>(100.)), AlmostEquals(quantity{1.}));
+    REQUIRE_THAT(sin(grad<>(200.)), AlmostEquals(quantity{0.}));
+    REQUIRE_THAT(sin(grad<>(300.)), AlmostEquals(quantity{-1.}));
+  }
+
+  SECTION("cos")
+  {
+    REQUIRE_THAT(cos(deg<>(0.)), AlmostEquals(quantity{1.}));
+    REQUIRE_THAT(cos(deg<>(90.)), AlmostEquals(quantity{0.}));
+    REQUIRE_THAT(cos(deg<>(180.)), AlmostEquals(quantity{-1.}));
+    REQUIRE_THAT(cos(deg<>(270.)), AlmostEquals(quantity{0.}));
+
+    REQUIRE_THAT(cos(grad<>(0.)), AlmostEquals(quantity{1.}));
+    REQUIRE_THAT(cos(grad<>(100.)), AlmostEquals(quantity{0.}));
+    REQUIRE_THAT(cos(grad<>(200.)), AlmostEquals(quantity{-1.}));
+    REQUIRE_THAT(cos(grad<>(300.)), AlmostEquals(quantity{0.}));
+  }
+
+  SECTION("tan")
+  {
+    REQUIRE_THAT(tan(deg<>(0.)), AlmostEquals(quantity{0.}));
+    REQUIRE_THAT(tan(deg<>(45.)), AlmostEquals(quantity{1.}));
+    REQUIRE_THAT(tan(deg<>(135.)), AlmostEquals(quantity{-1.}));
+    REQUIRE_THAT(tan(deg<>(180.)), AlmostEquals(quantity{0.}));
+
+    REQUIRE_THAT(tan(grad<>(0.)), AlmostEquals(quantity{0.}));
+    REQUIRE_THAT(tan(grad<>(50.)), AlmostEquals(quantity{1.}));
+    REQUIRE_THAT(tan(grad<>(150.)), AlmostEquals(quantity{-1.}));
+    REQUIRE_THAT(tan(grad<>(200.)), AlmostEquals(quantity{0.}));
+  }
+}
+
+TEST_CASE("inverse trigonometric functions", "[inv trig]")
+{
+  using namespace units::aliases;
+
+  SECTION("asin")
+  {
+    REQUIRE_THAT(asin(quantity{-1.}), AlmostEquals(deg<>(-90.)));
+    REQUIRE_THAT(asin(quantity{0.}), AlmostEquals(deg<>(0.)));
+    REQUIRE_THAT(asin(quantity{1.}), AlmostEquals(deg<>(90.)));
+  }
+
+  SECTION("acos")
+  {
+    REQUIRE_THAT(asin(quantity{-1.}), AlmostEquals(deg<>(-90.)));
+    REQUIRE_THAT(asin(quantity{0.}), AlmostEquals(deg<>(0.)));
+    REQUIRE_THAT(asin(quantity{1.}), AlmostEquals(deg<>(90.)));
+  }
+
+  SECTION("atan")
+  {
+    REQUIRE_THAT(atan(quantity{-1.}), AlmostEquals(deg<>(-45.)));
+    REQUIRE_THAT(atan(quantity{0.}), AlmostEquals(deg<>(0.)));
+    REQUIRE_THAT(atan(quantity{1.}), AlmostEquals(deg<>(45.)));
+  }
+}