terminal: test Screen.select frees existing pins

src/terminal/Screen.zig

@@ -7652,6 +7652,32 @@ test "Screen: select untracked" {
     try testing.expectEqual(tracked, s.pages.countTrackedPins());
 }
 
+test "Screen: select replaces existing pins" {
+    const testing = std.testing;
+    const alloc = testing.allocator;
+
+    var s = try init(alloc, .{ .cols = 10, .rows = 10, .max_scrollback = 0 });
+    defer s.deinit();
+    try s.testWriteString("ABC  DEF\n 123\n456");
+
+    const tracked = s.pages.countTrackedPins();
+    try s.select(Selection.init(
+        s.pages.pin(.{ .active = .{ .x = 0, .y = 0 } }).?,
+        s.pages.pin(.{ .active = .{ .x = 3, .y = 0 } }).?,
+        false,
+    ));
+    try testing.expectEqual(tracked + 2, s.pages.countTrackedPins());
+
+    // Replacing the selection must untrack the prior selection's pins
+    // rather than leak them.
+    try s.select(Selection.init(
+        s.pages.pin(.{ .active = .{ .x = 0, .y = 1 } }).?,
+        s.pages.pin(.{ .active = .{ .x = 2, .y = 1 } }).?,
+        false,
+    ));
+    try testing.expectEqual(tracked + 2, s.pages.countTrackedPins());
+}
+
 test "Screen: selectAll" {
     const testing = std.testing;
     const alloc = testing.allocator;