From ab0204f3dc517f8367f6ebfcb0abf0f622b26718 Mon Sep 17 00:00:00 2001
From: Graham McIntire <graham@mcintire.me>
Date: Thu, 23 Apr 2026 15:14:05 -0500
Subject: [PATCH] test: add StreamData properties for Aprsme.GeoUtils

Four properties exercise haversine_distance / significant_movement?:

- non-negativity across any in-range coordinate pair
- symmetry: d(a, b) == d(b, a) within a tight tolerance
- identity: d(p, p) == 0.0
- significance agrees with (haversine > threshold) for any integer
  threshold in 1..1000

Total: +4 properties, coverage stays clean (dialyzer: 0 new errors).
---
 test/aprsme/geo_utils_test.exs | 51 ++++++++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)

diff --git a/test/aprsme/geo_utils_test.exs b/test/aprsme/geo_utils_test.exs
index e9199a1..5279589 100644
--- a/test/aprsme/geo_utils_test.exs
+++ b/test/aprsme/geo_utils_test.exs
@@ -1,5 +1,6 @@
 defmodule Aprsme.GeoUtilsTest do
   use ExUnit.Case, async: true
+  use ExUnitProperties
 
   alias Aprsme.GeoUtils
 
@@ -78,4 +79,54 @@ defmodule Aprsme.GeoUtilsTest do
       refute GeoUtils.significant_movement?(33.16961, -96.4921, 33.16962, nil)
     end
   end
+
+  describe "property: haversine_distance" do
+    property "is always non-negative for numeric inputs" do
+      check all(
+              lat1 <- float(min: -89.0, max: 89.0),
+              lon1 <- float(min: -179.0, max: 179.0),
+              lat2 <- float(min: -89.0, max: 89.0),
+              lon2 <- float(min: -179.0, max: 179.0)
+            ) do
+        assert GeoUtils.haversine_distance(lat1, lon1, lat2, lon2) >= 0
+      end
+    end
+
+    property "is symmetric: d(a,b) == d(b,a)" do
+      check all(
+              lat1 <- float(min: -89.0, max: 89.0),
+              lon1 <- float(min: -179.0, max: 179.0),
+              lat2 <- float(min: -89.0, max: 89.0),
+              lon2 <- float(min: -179.0, max: 179.0)
+            ) do
+        a = GeoUtils.haversine_distance(lat1, lon1, lat2, lon2)
+        b = GeoUtils.haversine_distance(lat2, lon2, lat1, lon1)
+        assert_in_delta a, b, 0.01
+      end
+    end
+
+    property "d(p, p) == 0" do
+      check all(
+              lat <- float(min: -89.0, max: 89.0),
+              lon <- float(min: -179.0, max: 179.0)
+            ) do
+        assert GeoUtils.haversine_distance(lat, lon, lat, lon) == 0.0
+      end
+    end
+  end
+
+  describe "property: significant_movement?" do
+    property "agrees with the haversine + threshold check" do
+      check all(
+              lat1 <- float(min: -89.0, max: 89.0),
+              lon1 <- float(min: -179.0, max: 179.0),
+              lat2 <- float(min: -89.0, max: 89.0),
+              lon2 <- float(min: -179.0, max: 179.0),
+              threshold <- integer(1..1000)
+            ) do
+        d = GeoUtils.haversine_distance(lat1, lon1, lat2, lon2)
+        assert GeoUtils.significant_movement?(lat1, lon1, lat2, lon2, threshold) == d > threshold
+      end
+    end
+  end
 end