diff --git a/tests/custom_interval_tests.hpp b/tests/custom_interval_tests.hpp
new file mode 100644
index 0000000..8c97518
--- /dev/null
+++ b/tests/custom_interval_tests.hpp
@@ -0,0 +1,152 @@
+#pragma once
+
+#include "test_utility.hpp"
+#include "multi_join_interval.hpp"
+
+#include <ctime>
+#include <random>
+#include <cmath>
+#include <functional>
+
+class CustomIntervalTests : public ::testing::Test
+{};
+
+template <typename numerical_type, typename interval_kind_ = lib_interval_tree::closed>
+struct custom_interval : public lib_interval_tree::interval<numerical_type, interval_kind_>
+{
+  public:
+    using value_type = numerical_type;
+    using interval_kind = interval_kind_;
+
+    using lib_interval_tree::interval<numerical_type, interval_kind_>::low_;
+    using lib_interval_tree::interval<numerical_type, interval_kind_>::high_;
+
+    /**
+     *  Constructs an custom_interval. low MUST be smaller than high.
+     */
+    custom_interval(value_type low, value_type high)
+        : lib_interval_tree::interval<numerical_type, interval_kind_>{low, high}
+    {}
+
+    std::function<bool(value_type, value_type)> on_overlaps;
+    bool overlaps(custom_interval const& other) const
+    {
+        if (on_overlaps)
+            return on_overlaps(other.low_, other.high_);
+        return interval_kind::overlaps(low_, high_, other.low_, other.high_);
+    }
+
+    std::function<bool(custom_interval const& other)> on_overlaps_exclusive_ival;
+    bool overlaps_exclusive(custom_interval const& other) const
+    {
+        if (on_overlaps_exclusive_ival)
+            return on_overlaps_exclusive_ival(other);
+        return low_ < other.high_ && other.low_ < high_;
+    }
+
+    std::function<custom_interval(custom_interval const& other)> on_join;
+    custom_interval join(custom_interval const& other) const
+    {
+        if (on_join)
+            return on_join(other);
+        return {std::min(low_, other.low_), std::max(high_, other.high_)};
+    }
+};
+
+struct minimal_custom_interval : public lib_interval_tree::interval<int, lib_interval_tree::closed>
+{
+    using lib_interval_tree::interval<int, lib_interval_tree::closed>::interval;
+
+    minimal_custom_interval join(minimal_custom_interval const& other) const
+    {
+        return {std::min(low_, other.low_), std::max(high_, other.high_)};
+    }
+};
+
+TEST_F(CustomIntervalTests, CanInsertCustomIntervalJoined)
+{
+    lib_interval_tree::interval_tree<custom_interval<int>> tree;
+    tree.insert({0, 5});
+    tree.insert_overlap({4, 10});
+
+    ASSERT_EQ(tree.size(), 1);
+    EXPECT_EQ(tree.begin()->low(), 0);
+    EXPECT_EQ(tree.begin()->high(), 10);
+}
+
+TEST_F(CustomIntervalTests, CustomJoinIsCalled)
+{
+    lib_interval_tree::interval_tree<custom_interval<int>> tree;
+    auto ival1 = custom_interval<int>{0, 5};
+    auto ival2 = custom_interval<int>{4, 10};
+
+    bool join_called = false;
+    ival1.on_join = [&](custom_interval<int> const& other) -> custom_interval<int> {
+        join_called = true;
+        return {std::min(ival1.low_, other.low_), std::max(ival1.high_, other.high_)};
+    };
+
+    tree.insert(ival1);
+    tree.insert_overlap(ival2);
+
+    EXPECT_TRUE(join_called);
+}
+
+TEST_F(CustomIntervalTests, CustomOverlapsIsCalled)
+{
+    lib_interval_tree::interval_tree<custom_interval<int>> tree;
+    auto ival1 = custom_interval<int>{0, 5};
+    auto ival2 = custom_interval<int>{4, 10};
+
+    bool overlaps_called = false;
+    ival1.on_overlaps = [&](int l, int h) -> bool {
+        overlaps_called = true;
+        return custom_interval<int>::interval_kind::overlaps(ival1.low_, ival1.high_, l, h);
+    };
+
+    tree.insert(ival1);
+    tree.insert_overlap(ival2);
+
+    EXPECT_TRUE(overlaps_called);
+}
+
+TEST_F(CustomIntervalTests, CustomOverlapsExclusiveIvalIsCalled)
+{
+    lib_interval_tree::interval_tree<custom_interval<int>> tree;
+    auto ival1 = custom_interval<int>{0, 5};
+    auto ival2 = custom_interval<int>{4, 10};
+
+    bool overlaps_exclusive_ival_called = false;
+    ival1.on_overlaps_exclusive_ival = [&](custom_interval<int> const& other) -> bool {
+        overlaps_exclusive_ival_called = true;
+        return ival1.low_ < other.high_ && other.low_ < ival1.high_;
+    };
+
+    tree.insert(ival1);
+    tree.insert_overlap(ival2, true);
+
+    EXPECT_TRUE(overlaps_exclusive_ival_called);
+}
+
+TEST_F(CustomIntervalTests, CanUseMinimalCustomInterval)
+{
+    lib_interval_tree::interval_tree<minimal_custom_interval> tree;
+    tree.insert({0, 5});
+    tree.insert_overlap({4, 10});
+    tree.erase(tree.begin());
+
+    EXPECT_EQ(tree.size(), 0);
+
+    tree.insert({0, 5});
+    tree.insert({7, 10});
+    auto iter = tree.find({0, 5});
+    ASSERT_NE(iter, tree.end());
+    EXPECT_EQ(iter->low(), 0);
+    EXPECT_EQ(iter->high(), 5);
+
+    tree.deoverlap();
+    auto iter2 = tree.overlap_find({8, 12});
+    ASSERT_NE(iter2, tree.end());
+    EXPECT_EQ(iter2->low(), 7);
+    EXPECT_EQ(iter2->high(), 10);
+}
\ No newline at end of file
diff --git a/tests/tests.cpp b/tests/tests.cpp
index def3a02..de6ab1a 100644
--- a/tests/tests.cpp
+++ b/tests/tests.cpp
@@ -14,6 +14,7 @@
 #include "float_overlap_tests.hpp"
 #include "iteration_tests.hpp"
 #include "hook_tests.hpp"
+#include "custom_interval_tests.hpp"
 
 int main(int argc, char** argv)
 {