Sketcher: Add gtest unit test framework

tests/src/Mod/Sketcher/App/CMakeLists.txt

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+add_subdirectory(planegcs)

tests/src/Mod/Sketcher/App/planegcs/CMakeLists.txt

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+target_sources(
+    Sketcher_tests_run
+        PRIVATE
+            ${CMAKE_CURRENT_SOURCE_DIR}/GCS.cpp
+)

tests/src/Mod/Sketcher/App/planegcs/GCS.cpp

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+// SPDX-License-Identifier: LGPL-2.1-or-later
+
+#include "gtest/gtest.h"
+
+#include "Mod/Sketcher/App/planegcs/GCS.h"
+
+class SystemTest : public GCS::System{
+public:
+    size_t getNumberOfConstraints(int tagID = -1) {
+        return _getNumberOfConstraints(tagID);
+    }
+};
+
+class GCSTest: public ::testing::Test
+{
+protected:
+    void SetUp() override
+    {
+        _system = std::make_unique<SystemTest>();
+    }
+
+    void TearDown() override
+    {
+        _system.reset();
+    }
+
+    SystemTest* System()
+    {
+        return _system.get();
+    }
+
+private:
+    std::unique_ptr<SystemTest> _system;
+};
+
+TEST_F(GCSTest, clearConstraints) // NOLINT
+{
+    // Arrange
+    const size_t numConstraints {100};
+    for (size_t i = 0; i < numConstraints; ++i) {
+        System()->addConstraint(new GCS::Constraint());
+    }
+    ASSERT_EQ(numConstraints, System()->getNumberOfConstraints());
+
+    // Act
+    System()->clear();
+
+    // Assert
+    EXPECT_EQ(0, System()->getNumberOfConstraints());
+}

tests/src/Mod/Sketcher/CMakeLists.txt

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+add_subdirectory(App)