Add unit tests for DistanceCalculator

app/src/test/java/org/nitri/opentopo/DistanceCalculatorTest.kt

@@ -0,0 +1,33 @@
+package org.nitri.opentopo
+
+import org.junit.Assert.assertEquals
+import org.junit.Test
+import org.nitri.opentopo.util.DistanceCalculator
+
+class DistanceCalculatorTest {
+
+    @Test
+    fun distanceReturnsZeroForIdenticalPoints() {
+        val latitude = 48.8566
+        val longitude = 2.3522
+
+        val distance = DistanceCalculator.distance(latitude, longitude, latitude, longitude)
+
+        assertEquals(0.0, distance, 0.0)
+    }
+
+    @Test
+    fun distanceMatchesExpectedValueForKnownCoordinates() {
+        val parisLat = 48.8566
+        val parisLon = 2.3522
+        val londonLat = 51.5074
+        val londonLon = -0.1278
+
+        val distance = DistanceCalculator.distance(parisLat, parisLon, londonLat, londonLon)
+
+        val expectedDistanceMeters = 343_556.0
+        val toleranceMeters = 1_000.0
+
+        assertEquals(expectedDistanceMeters, distance, toleranceMeters)
+    }
+}