diff --git a/src/main/java/io/github/js0ny/ilp_coursework/service/GpsCalculationService.java b/src/main/java/io/github/js0ny/ilp_coursework/service/GpsCalculationService.java
index 0cf07f8..a27243a 100644
--- a/src/main/java/io/github/js0ny/ilp_coursework/service/GpsCalculationService.java
+++ b/src/main/java/io/github/js0ny/ilp_coursework/service/GpsCalculationService.java
@@ -40,6 +40,7 @@ public class GpsCalculationService {
     public double calculateDistance(LngLatDto position1, LngLatDto position2) {
         double lngDistance = position2.lng() - position1.lng();
         double latDistance = position2.lat() - position1.lat();
+        //  Euclidean: \sqrt{a^2 + b^2}
         return Math.sqrt(lngDistance * lngDistance + latDistance * latDistance);
     }
 
@@ -70,7 +71,7 @@ public class GpsCalculationService {
      * @see io.github.js0ny.ilp_coursework.controller.ApiController#getNextPosition(MovementRequestDto)
      */
     public LngLatDto nextPosition(LngLatDto start, double angle) {
-        double rad = Math.toRadians(angle);
+        double rad = Math.toRadians(angle); // Convert to radian for Java triangle function calculation
         double newLng = Math.cos(rad) * STEP + start.lng();
         double newLat = Math.sin(rad) * STEP + start.lat();
         return new LngLatDto(newLng, newLat);
diff --git a/src/test/java/io/github/js0ny/ilp_coursework/service/GpsCalculationServiceTest.java b/src/test/java/io/github/js0ny/ilp_coursework/service/GpsCalculationServiceTest.java
index 0e46370..4f8a52d 100644
--- a/src/test/java/io/github/js0ny/ilp_coursework/service/GpsCalculationServiceTest.java
+++ b/src/test/java/io/github/js0ny/ilp_coursework/service/GpsCalculationServiceTest.java
@@ -10,6 +10,7 @@ import org.junit.jupiter.api.Test;
 import java.util.List;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.assertj.core.api.AssertionsForClassTypes.within;
 
 
@@ -350,5 +351,25 @@ public class GpsCalculationServiceTest {
             boolean actual = service.checkIsInRegion(position, RECTANGLE_REGION);
             assertThat(actual).isEqualTo(expected);
         }
+
+        @Test
+        @DisplayName("Edge Case: Region not forming polygon")
+        void isInRegion_shouldThrowExceptions_whenRegionNotFormingPolygon() {
+            var position = new LngLatDto(2.0, 2.0);
+            var region = new RegionDto("line", List.of(new LngLatDto(0.0, 0.0), new LngLatDto(0.0001, 0.0), new LngLatDto(0.0, 0.0)));
+            assertThatThrownBy(() -> {
+                service.checkIsInRegion(position, region);
+            }).isInstanceOf(IllegalArgumentException.class).hasMessage("Region is not closed.");
+        }
+
+        @Test
+        @DisplayName("Edge Case: Region is not closed")
+        void isInRegion_shouldThrowExceptions_whenRegionNotClose() {
+            var position = new LngLatDto(2.0, 2.0);
+            var region = new RegionDto("rectangle", List.of(new LngLatDto(0.0, 0.0), new LngLatDto(2.0, 0.0), new LngLatDto(2.0, 2.0), new LngLatDto(0.0, 2.0), new LngLatDto(0.0, -1.0)));
+            assertThatThrownBy(() -> {
+                service.checkIsInRegion(position, region);
+            }).isInstanceOf(IllegalArgumentException.class).hasMessage("Region is not closed.");
+        }
     }
 }
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