diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index feb385dec..01f5b28b2 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -146,6 +146,7 @@ TEST(TestQPrefProxy testqPrefProxy.cpp)
 TEST(TestQPrefTechnicalDetails testqPrefTechnicalDetails.cpp)
 TEST(TestQPrefUnits testqPrefUnits.cpp)
 TEST(TestQPrefUpdateManager testqPrefUpdateManager.cpp)
+TEST(TestformatDiveGasString testformatDiveGasString.cpp)
 add_test(NAME TestQML COMMAND $<TARGET_FILE:TestQML> -input ${SUBSURFACE_SOURCE}/tests)
 
 # this is currently broken
diff --git a/tests/testformatDiveGasString.cpp b/tests/testformatDiveGasString.cpp
new file mode 100644
index 000000000..14ab4923a
--- /dev/null
+++ b/tests/testformatDiveGasString.cpp
@@ -0,0 +1,173 @@
+#include "testformatDiveGasString.h"
+
+#include "../core/dive.h"
+#include "../core/string-format.h"
+
+void TestformatDiveGasString::init()
+{
+}
+
+void TestformatDiveGasString::test_empty()
+{
+	struct dive dive = {0};
+
+	QCOMPARE(formatDiveGasString(&dive), "air");
+}
+
+void TestformatDiveGasString::test_air()
+{
+	struct dive dive = {0};
+	cylinder_t *cylinder = get_or_create_cylinder(&dive, 0);
+
+	cylinder->start.mbar = 230000;
+	cylinder->end.mbar = 100000;
+
+	QCOMPARE(formatDiveGasString(&dive), "air");
+}
+
+void TestformatDiveGasString::test_nitrox() {
+	struct dive dive = {0};
+	cylinder_t *cylinder = get_or_create_cylinder(&dive, 0);
+
+	cylinder->gasmix.o2.permille = 320;
+	cylinder->start.mbar = 230000;
+	cylinder->end.mbar = 100000;
+
+	QCOMPARE(formatDiveGasString(&dive), "32%");
+}
+
+void TestformatDiveGasString::test_nitrox_not_use() {
+	struct dive dive = {0};
+	cylinder_t *cylinder = get_or_create_cylinder(&dive, 0);
+
+	cylinder->gasmix.o2.permille = 320;
+	cylinder->start.mbar = 230000;
+	cylinder->end.mbar = 100000;
+
+	cylinder = get_or_create_cylinder(&dive, 1);
+
+	cylinder->gasmix.o2.permille = 1000;
+	cylinder->cylinder_use = NOT_USED;
+	cylinder->start.mbar = 230000;
+	cylinder->end.mbar = 100000;
+
+	QCOMPARE(formatDiveGasString(&dive), "32%");
+}
+
+void TestformatDiveGasString::test_nitrox_deco() {
+	struct dive dive = {0};
+	cylinder_t *cylinder = get_or_create_cylinder(&dive, 0);
+
+	cylinder->gasmix.o2.permille = 320;
+	cylinder->start.mbar = 230000;
+	cylinder->end.mbar = 100000;
+
+	cylinder = get_or_create_cylinder(&dive, 1);
+
+	cylinder->gasmix.o2.permille = 1000;
+	cylinder->start.mbar = 230000;
+	cylinder->end.mbar = 100000;
+
+	QCOMPARE(formatDiveGasString(&dive), QString("32…100%"));
+}
+
+void TestformatDiveGasString::test_reverse_nitrox_deco() {
+	struct dive dive = {0};
+	cylinder_t *cylinder = get_or_create_cylinder(&dive, 0);
+
+	cylinder->gasmix.o2.permille = 1000;
+	cylinder->start.mbar = 230000;
+	cylinder->end.mbar = 100000;
+
+	cylinder = get_or_create_cylinder(&dive, 1);
+
+	cylinder->gasmix.o2.permille = 270;
+	cylinder->start.mbar = 230000;
+	cylinder->end.mbar = 100000;
+
+	QCOMPARE(formatDiveGasString(&dive), QString("27…100%"));
+}
+
+void TestformatDiveGasString::test_trimix() {
+	struct dive dive = {0};
+	cylinder_t *cylinder = get_or_create_cylinder(&dive, 0);
+
+	cylinder->gasmix.o2.permille = 210;
+	cylinder->gasmix.he.permille = 350;
+	cylinder->start.mbar = 230000;
+	cylinder->end.mbar = 100000;
+
+	QCOMPARE(formatDiveGasString(&dive), "21/35");
+}
+
+void TestformatDiveGasString::test_trimix_deco() {
+	struct dive dive = {0};
+	cylinder_t *cylinder = get_or_create_cylinder(&dive, 0);
+
+	cylinder->gasmix.o2.permille = 210;
+	cylinder->gasmix.he.permille = 350;
+	cylinder->start.mbar = 230000;
+	cylinder->end.mbar = 100000;
+
+	cylinder = get_or_create_cylinder(&dive, 1);
+
+	cylinder->gasmix.o2.permille = 500;
+	cylinder->gasmix.he.permille = 200;
+	cylinder->start.mbar = 230000;
+	cylinder->end.mbar = 100000;
+
+	cylinder = get_or_create_cylinder(&dive, 2);
+
+	cylinder->gasmix.o2.permille = 1000;
+	cylinder->start.mbar = 230000;
+	cylinder->end.mbar = 100000;
+
+	QCOMPARE(formatDiveGasString(&dive), "21/35…100%");
+}
+
+void TestformatDiveGasString::test_reverse_trimix_deco() {
+	struct dive dive = {0};
+	cylinder_t *cylinder = get_or_create_cylinder(&dive, 0);
+
+	cylinder->gasmix.o2.permille = 1000;
+	cylinder->start.mbar = 230000;
+	cylinder->end.mbar = 100000;
+
+	cylinder = get_or_create_cylinder(&dive, 1);
+
+	cylinder->gasmix.o2.permille = 500;
+	cylinder->gasmix.he.permille = 200;
+	cylinder->start.mbar = 230000;
+	cylinder->end.mbar = 100000;
+
+	cylinder = get_or_create_cylinder(&dive, 2);
+
+	cylinder->gasmix.o2.permille = 210;
+	cylinder->gasmix.he.permille = 350;
+	cylinder->start.mbar = 230000;
+	cylinder->end.mbar = 100000;
+
+	QCOMPARE(formatDiveGasString(&dive), "21/35…100%");
+}
+
+void TestformatDiveGasString::test_ccr() {
+	struct dive dive = {0};
+	cylinder_t *cylinder = get_or_create_cylinder(&dive, 0);
+
+	cylinder->gasmix.o2.permille = 1000;
+	cylinder->cylinder_use = OXYGEN;
+	cylinder->start.mbar = 230000;
+	cylinder->end.mbar = 100000;
+
+	cylinder = get_or_create_cylinder(&dive, 1);
+
+	cylinder->gasmix.o2.permille = 210;
+	cylinder->gasmix.he.permille = 350;
+	cylinder->cylinder_use = DILUENT;
+	cylinder->start.mbar = 230000;
+	cylinder->end.mbar = 100000;
+
+	QCOMPARE(formatDiveGasString(&dive), "21/35");
+}
+
+QTEST_GUILESS_MAIN(TestformatDiveGasString)
diff --git a/tests/testformatDiveGasString.h b/tests/testformatDiveGasString.h
new file mode 100644
index 000000000..21951b437
--- /dev/null
+++ b/tests/testformatDiveGasString.h
@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <QtTest>
+
+class TestformatDiveGasString : public QObject {
+	Q_OBJECT
+private slots:
+	void init();
+	void test_empty();
+	void test_air();
+	void test_nitrox();
+	void test_nitrox_not_use();
+	void test_nitrox_deco();
+	void test_reverse_nitrox_deco();
+	void test_trimix();
+	void test_trimix_deco();
+	void test_reverse_trimix_deco();
+	void test_ccr();
+};