r.distance: Add tests for r.distance module (OSGeo#4679)

* Add testsuite files for r.distance

* Added function descriptions

* Stripped Carriage Returns for windows-2019 build and tests

* Changed maps and tuned asserts to rectify earlier build fails

* Corrected maps in 3rd test

* fix for windows build issues and doc correction

raster/r.distance/testsuite/test_distance.py

@@ -0,0 +1,81 @@
+from grass.gunittest.case import TestCase
+from grass.gunittest.main import test
+from grass.gunittest.gmodules import SimpleModule
+
+
+class TestRDistance(TestCase):
+
+    @classmethod
+    def setUpClass(cls):
+        """Set up a temporary region and generate test data."""
+        cls.use_temp_region()
+        cls.runModule("g.region", n=10, s=0, e=10, w=0, res=1)
+        # Create 'map1' with a block at the top-left corner
+        cls.runModule(
+            "r.mapcalc",
+            expression="map1 = if(row() <= 2 && col() <= 2, 1, null())",
+            overwrite=True,
+        )
+        # Create 'map2' with a block in the center
+        cls.runModule(
+            "r.mapcalc",
+            expression="map2 = if(row() >= 4 && row() <=6 && col() >= 4 && col() <= 6, 1, null())",
+            overwrite=True,
+        )
+        cls.runModule("r.mapcalc", expression="map3 = null()", overwrite=True)
+
+    @classmethod
+    def tearDownClass(cls):
+        """Clean up after tests."""
+        cls.runModule(
+            "g.remove", flags="f", type="raster", name=["map1", "map2", "map3"]
+        )
+        cls.del_temp_region()
+
+    def test_distance(self):
+        """Test distance calculation between map1 and map2."""
+        module = SimpleModule("r.distance", map=("map1", "map2"))
+        self.assertModule(module)
+
+        result = module.outputs.stdout.strip().splitlines()
+
+        expected_results = ["1:1:2.8284271247:1.5:8.5:3.5:6.5"]
+
+        for i, component in enumerate(result):
+            self.assertEqual(
+                component, expected_results[i], f"Mismatch at line {i + 1}"
+            )
+
+    def test_overlap_distance(self):
+        """Test r.distance when comparing a map to itself with overlapping features."""
+        module = SimpleModule("r.distance", map=("map1", "map1"), flags="o")
+        self.assertModule(module)
+
+        result = module.outputs.stdout.strip().splitlines()
+
+        expected_results = ["1:1:0:0.5:9.5:0.5:9.5"]
+
+        self.assertEqual(
+            result,
+            expected_results,
+            "Mismatch in r.distance output for overlapping features",
+        )
+
+    def test_null_distance(self):
+        """Test r.distance when reporting null values with -n flag."""
+        module = SimpleModule("r.distance", map=("map3", "map2"), flags="n")
+        self.assertModule(module)
+
+        result = module.outputs.stdout.strip().splitlines()
+
+        expected_results = ["*:*:0:0.5:9.5:0.5:9.5", "*:1:2:3.5:8.5:3.5:6.5"]
+
+        self.assertEqual(
+            result,
+            expected_results,
+            "Mismatch in r.distance output for reporting null objects as *",
+        )
+
+
+if __name__ == "__main__":
+    test()