feat: trapping rain water problem done

tests/test_essentials.py

@@ -25,3 +25,17 @@ def test_find_missing():
 	result = find_missing(input)
 	expected = 4
 	assert result == expected
+
+def test_rain_watter():
+	input = [3,0,1,0,4,0,2]
+	expected = 10
+	result = trap_rain_water(input)
+	assert result == expected
+	input = [3,0,2,0,4]
+	expected = 7
+	result = trap_rain_water(input)
+	assert result == expected
+	input = [1,2,3,4]
+	expected = 0
+	result = trap_rain_water(input)
+	assert result == expected