SHAPE_ARC: Expose bug introduced by 5813164d1 in tests

The angle needs to be added to the start angle.

Add tests to cover this:

* Check end point is correct
* Check midpoints are within tolerance

This would have prevented the bug fixed in 5813164d1,
as well as the bug fixed in this commit.

As well as failed tests, this manifests when routing across
Edge.Cuts arcs (unless they happen to start at 0 degrees
staritng angle).

Expose as expected failure to prove tests catch it.
Fix to follow in separate commit.

(cherry picked from commit 183f4fe9a5)

qa/common/geometry/test_shape_arc.cpp

@@ -301,7 +301,7 @@ struct ARC_TO_POLYLINE_CASE
  * @param  aTolEnds  the tolerance for the endpoint-centre distance
  * @return           true if predicate met
  */
-bool ArePolylinePointsNearCircle(
+bool ArePolylineEndPointsNearCircle(
         const SHAPE_LINE_CHAIN& aPolyline, const VECTOR2I& aCentre, int aRad, int aTolEnds )
 {
     std::vector<VECTOR2I> points;
@@ -314,8 +314,33 @@ bool ArePolylinePointsNearCircle(
     return GEOM_TEST::ArePointsNearCircle( points, aCentre, aRad, aTolEnds );
 }
 
+/**
+ * Predicate for checking a polyline has all the segment mid points on
+ * (near) a circle of given centre and radius
+ * @param  aPolyline the polyline to check
+ * @param  aCentre   the circle centre
+ * @param  aRad      the circle radius
+ * @param  aTolEnds  the tolerance for the midpoint-centre distance
+ * @return           true if predicate met
+ */
+bool ArePolylineMidPointsNearCircle(
+        const SHAPE_LINE_CHAIN& aPolyline, const VECTOR2I& aCentre, int aRad, int aTolMidPts )
+{
+    std::vector<VECTOR2I> points;
 
-BOOST_AUTO_TEST_CASE( ArcToPolyline )
+    for( int i = 0; i < aPolyline.PointCount() - 1; ++i )
+    {
+        const VECTOR2I mid_pt = ( aPolyline.CPoint( i ) + aPolyline.CPoint( i + 1 ) ) / 2;
+        points.push_back( mid_pt );
+    }
+
+    return GEOM_TEST::ArePointsNearCircle( points, aCentre, aRad, aTolMidPts );
+}
+
+#ifdef HAVE_EXPECTED_FAILURES
+
+// Start and end point check fail for the 3 non-zero radius cases
+BOOST_AUTO_TEST_CASE( ArcToPolyline, *boost::unit_test::expected_failures( 3 * 2 ) )
 {
     const std::vector<ARC_TO_POLYLINE_CASE> cases = {
         {
@@ -335,11 +360,22 @@ BOOST_AUTO_TEST_CASE( ArcToPolyline )
             },
         },
         {
+            // check larger sizes still have required precisions
+            // and that reverse angles work too
             "Larger semicircle",
             {
                 { 0, 0 },
-                { -1000, 0 },
-                180,
+                { -10000, 0 },
+                -180,
+            },
+        },
+        {
+            // Make sure it doesn't only work for "easy" angles
+            "Non-round geometry",
+            {
+                { 0, 0 },
+                { -1234, 0 },
+                42.22,
             },
         },
     };
@@ -358,18 +394,28 @@ BOOST_AUTO_TEST_CASE( ArcToPolyline )
 
             BOOST_TEST_MESSAGE( "Polyline has " << chain.PointCount() << " points" );
 
+            const int pt_tol = 1;
+
+            // Start point where expected
             BOOST_CHECK_EQUAL( chain.CPoint( 0 ), c.m_geom.m_start_point );
 
+            // End point where expected
+            BOOST_CHECK_PREDICATE( KI_TEST::IsVecWithinTol<VECTOR2I>,
+                    ( chain.CPoint( -1 ) )( this_arc.GetP1() )( pt_tol ) );
+
             const int radius = ( c.m_geom.m_center_point - c.m_geom.m_start_point ).EuclideanNorm();
-            const int tol = 2;
 
-            BOOST_CHECK_PREDICATE( ArePolylinePointsNearCircle,
-                    ( chain )( c.m_geom.m_center_point )( radius )( tol ) );
+            const int ep_tol = 2;
+            BOOST_CHECK_PREDICATE( ArePolylineEndPointsNearCircle,
+                    ( chain )( c.m_geom.m_center_point )( radius )( ep_tol ) );
 
-            // TODO: check midpoints are near circle too
+            const int mp_tol = 3;
+            BOOST_CHECK_PREDICATE( ArePolylineMidPointsNearCircle,
+                    ( chain )( c.m_geom.m_center_point )( radius )( mp_tol ) );
         }
     }
 }
 
+#endif
 
 BOOST_AUTO_TEST_SUITE_END()