Switch screen functionality

There's 2 "screens" that I've called primary and secondary  here
Switching the screen allows doing things without impact the primary one

vim and less use this which is why when you quit you have no evidance of it

Author: mikeymike

src/UnixTerminal.php

@@ -229,6 +229,16 @@ public function moveCursorToColumn(int $column) : void
         $this->output->write(sprintf("\033[%dC", $column));
     }
 
+    public function showSecondaryScreen() : void
+    {
+        $this->output->write("\033[?47h");
+    }
+
+    public function showPrimaryScreen() : void
+    {
+        $this->output->write("\033[?47l");
+    }
+
     /**
      * Read bytes from the input stream
      */

test/UnixTerminalTest.php

@@ -229,6 +229,28 @@ public function testMoveCursorToColumn() : void
         self::assertEquals("\033[10C", $output->fetch());
     }
 
+    public function testShowAlternateScreen() : void
+    {
+        $input  = $this->createMock(InputStream::class);
+        $output = new BufferedOutput;
+
+        $terminal = new UnixTerminal($input, $output);
+        $terminal->showSecondaryScreen();
+
+        self::assertEquals("\033[?47h", $output->fetch());
+    }
+
+    public function testShowMainScreen() : void
+    {
+        $input  = $this->createMock(InputStream::class);
+        $output = new BufferedOutput;
+
+        $terminal = new UnixTerminal($input, $output);
+        $terminal->showPrimaryScreen();
+
+        self::assertEquals("\033[?47l", $output->fetch());
+    }
+
     public function testRead() : void
     {
         $tempStream = fopen('php://temp', 'r+');