fix for rivers and bridges snake start positions (#85)

* fix for rivers and bridges snake start positions

* update max player count, add unit test

* set player count to 12 (max for smallest size)

* fix: one of the 19x19 spawn points

* randomize snake placement at start positions

* randomly choose starts in quadrants

* fix: check that start positions are valid

* modify food placement to avoid hazards

maps/hazards_internal_test.go

@@ -0,0 +1,46 @@
+package maps
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/BattlesnakeOfficial/rules"
+	"github.com/stretchr/testify/require"
+)
+
+func TestRiversAndBridgesSnakePlacement(t *testing.T) {
+	m := RiverAndBridgesHazardsMap{}
+	settings := rules.Settings{}
+
+	// check all the supported sizes
+	for _, size := range []int{11, 19, 25} {
+		initialState := rules.NewBoardState(size, size)
+		startPositions := riversAndBridgesStartPositions[rules.Point{X: size, Y: size}]
+		maxSnakes := len(startPositions)
+		for i := 0; i < maxSnakes; i++ {
+			initialState.Snakes = append(initialState.Snakes, rules.Snake{ID: fmt.Sprint(i), Body: []rules.Point{}})
+		}
+
+		nextState := rules.NewBoardState(size, size)
+		editor := NewBoardStateEditor(nextState)
+		err := m.SetupBoard(initialState, settings, editor)
+		require.NoError(t, err)
+		for _, s := range nextState.Snakes {
+			require.Len(t, s.Body, rules.SnakeStartSize, "Placed snakes should have the right length")
+			require.Equal(t, s.Health, rules.SnakeMaxHealth, "Placed snakes should have the right health")
+			require.NotEmpty(t, s.ID, "Snake ID shouldn't be empty (should get copied when placed)")
+
+			// Check that the snake is placed at one of the specified start positions
+			validStart := false
+			for _, q := range startPositions {
+				for i := 0; i < len(q); i++ {
+					if q[i].X == s.Body[0].X && q[i].Y == s.Body[0].Y {
+						validStart = true
+						break
+					}
+				}
+			}
+			require.True(t, validStart, "Snake must be placed in one of the specified start positions")
+		}
+	}
+}