diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 03cb235..bdd92c3 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -1,4 +1,4 @@
-name: Build SeBa
+name: Build and test SeBa
 
 on:
   push:
@@ -19,3 +19,7 @@ jobs:
       run: |
         cd dstar
         make
+    - name: Build and run unit tests
+      run: |
+        git submodule update --init --recursive
+        make test
\ No newline at end of file
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..58750c4
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,9 @@
+Makefile.inc
+dstar/Makefile.inc
+**/*.o
+**/*.a
+starev
+dstar/Normalisation
+dstar/SeBa
+**/*.data
+build/
diff --git a/.gitmodules b/.gitmodules
new file mode 100644
index 0000000..5a4e85a
--- /dev/null
+++ b/.gitmodules
@@ -0,0 +1,3 @@
+[submodule "third_party/googletest"]
+	path = third_party/googletest
+	url = https://github.com/google/googletest.git
diff --git a/Makefile b/Makefile
index 290352b..8e76218 100644
--- a/Makefile
+++ b/Makefile
@@ -9,7 +9,7 @@ DIRS	= node std sstar dstar rdc
 
 all:	lib $(EXE)
 
-test:
+test-compiler:
 	echo $(CXX)
 	echo `which $(CXX)`
 
@@ -22,3 +22,53 @@ lib:	Makefile.inc
 clean:	Makefile.inc
 	@for d in $(DIRS) ; do echo '\nmake' $@ in $$d; make -C $$d $@ ; done
 	/bin/rm -f *~ $(EXE) Makefile.inc
+
+# --- Test support ---
+TEST_CXXFLAGS = $(CXXFLAGS) -std=c++23
+TESTDIR   = tests
+BUILDDIR  = build
+TESTBIN   = $(BUILDDIR)/run_tests
+TESTSRC   = $(wildcard $(TESTDIR)/*.cpp)
+TESTOBJ   = $(patsubst $(TESTDIR)/%.cpp,$(BUILDDIR)/%.o,$(TESTSRC))
+
+GTEST_DIR = third_party/googletest/googletest
+GTEST_SRC = $(GTEST_DIR)/src/gtest-all.cc
+GTEST_OBJ = $(BUILDDIR)/gtest-all.o
+GTEST_INC = -I$(GTEST_DIR)/include -I$(GTEST_DIR)
+GTEST_MAIN_SRC = $(GTEST_DIR)/src/gtest_main.cc
+GTEST_MAIN_OBJ = $(BUILDDIR)/gtest_main.o
+
+# Create build directory
+$(BUILDDIR):
+	mkdir -p $(BUILDDIR)
+
+# Compile Google Test source
+$(GTEST_OBJ): $(GTEST_SRC) | $(BUILDDIR)
+	$(CXX) $(TEST_CXXFLAGS) $(GTEST_INC) -c $< -o $@
+
+# Compile test sources
+$(BUILDDIR)/%.o: $(TESTDIR)/%.cpp | $(BUILDDIR)
+	$(CXX) $(TEST_CXXFLAGS) $(GTEST_INC) -I./include -c $< -o $@
+
+# Compile Google Test main
+$(GTEST_MAIN_OBJ): $(GTEST_MAIN_SRC) | $(BUILDDIR)
+	$(CXX) $(TEST_CXXFLAGS) $(GTEST_INC) -c $< -o $@
+
+# Link final test binary
+$(TESTBIN): $(TESTOBJ) $(GTEST_OBJ) $(GTEST_MAIN_OBJ)
+	$(CXX) $(TEST_CXXFLAGS) $(GTEST_INC) -I./include $^ \
+	    $(LDLIBS) -lpthread -o $@
+
+# Run tests
+test: $(TESTBIN)
+	@echo "Running unit tests..."
+	@./$(TESTBIN)
+
+# Run specific tests matching a pattern
+test_%: $(TESTBIN)
+	@echo "Running tests matching '$*'..."
+	@./$(TESTBIN) --gtest_filter=*${*}*
+
+# Optional cleanup
+clean-tests:
+	/bin/rm -rf $(BUILDDIR)
diff --git a/tests/README.md b/tests/README.md
new file mode 100644
index 0000000..63b0e36
--- /dev/null
+++ b/tests/README.md
@@ -0,0 +1,78 @@
+# Tests
+
+## Overview
+
+Unit tests live in the `tests/` directory.
+They use **GoogleTest (gtest)**, a lightweight C++ testing framework.
+Tests are built and executed by running:
+
+``` sh
+make test
+```
+
+
+This compiles all test files (`tests/*.cpp`), links them against project libraries and gtest, and runs them automatically.
+Passing tests will print `[ PASSED ]` lines in the terminal.
+
+## Getting GoogleTest Source
+
+This project vendors GoogleTest to make the test build self-contained.
+Ensure the submodules are cloned so that the GoogleTest code is included:
+
+```sh
+git submodule update --init --recursive
+```
+
+This will populate `third_party/googletest/`, which contains the GoogleTest source built automatically when running `make test`.
+
+## Cleaning Up
+
+To remove test binaries:
+
+``` sh
+make clean-tests
+```
+
+## Writing a Test
+
+Each test file is a small C++ program that includes both gtest and your project
+headers.
+
+You want to define test cases using the `TEST` macro provided by gtest, and
+ensure that your functions behave as expected using assertions like `EXPECT_EQ`, `ASSERT_TRUE`, etc.
+
+Example:
+
+``` cpp
+#include "util_math.h
+#include <gtest/gtest.h>
+
+TEST(Basic, Add) { EXPECT_EQ(add(2, 2), 4); }
+```
+
+## Running Tests
+
+Run all tests:
+
+``` sh
+make test
+```
+
+Run a specific test suite or test case:
+
+``` sh
+make test_[pattern]
+```
+
+E.g., run all tests marked `UtilMath`, run:
+
+``` sh
+make test_UtilMath
+
+```
+
+Run a specific test case within a suite:
+
+``` sh
+make test_UtilMath.Twiddles
+```
diff --git a/tests/test_basic.cpp b/tests/test_basic.cpp
new file mode 100644
index 0000000..f753908
--- /dev/null
+++ b/tests/test_basic.cpp
@@ -0,0 +1,5 @@
+#include <gtest/gtest.h>
+
+int add(int a, int b) { return a + b; }
+
+TEST(Basic, Add) { EXPECT_EQ(add(2, 2), 4); }
diff --git a/tests/test_util_math.cpp b/tests/test_util_math.cpp
new file mode 100644
index 0000000..f640961
--- /dev/null
+++ b/tests/test_util_math.cpp
@@ -0,0 +1,30 @@
+#include "util_math.h"
+#include <gtest/gtest.h>
+
+// basic numerical tolerance for comparisons
+static constexpr real EPS = 1e-12;
+
+TEST(UtilMath, Twiddles) {
+    EXPECT_TRUE(twiddles(1.0, 1.0 + 1e-13, EPS));
+    EXPECT_FALSE(twiddles(1.0, 1.1, EPS));
+}
+
+TEST(UtilMath, Sign) {
+    EXPECT_EQ(sign(3.5), 1);
+    EXPECT_EQ(sign(-2.1), -1);
+    EXPECT_EQ(sign(0.0), 0);
+}
+
+TEST(UtilMath, AdjustNumberToPower) {
+    // result should not exceed max_step_size
+    real result = adjust_number_to_power(5.5, 4.0);
+    EXPECT_LE(result, 4.0);
+}
+
+TEST(UtilMath, AsinhAcoshConsistency) {
+    real x = 1.5;
+    real s = sinh(x);
+    real c = cosh(x);
+    EXPECT_NEAR(asinh(s), x, 1e-12);
+    EXPECT_NEAR(acosh(c), x, 1e-12);
+}
diff --git a/third_party/googletest b/third_party/googletest
new file mode 160000
index 0000000..b2b9072
--- /dev/null
+++ b/third_party/googletest
@@ -0,0 +1 @@
+Subproject commit b2b9072ecbe874f5937054653ef8f2731eb0f010