patch 8.2.1508: not all debugger commands covered by tests

Problem:    Not all debugger commands covered by tests.
Solution:   Add tests for going up/down in the stack. (Ben Jackson,
            closes #6765)
diff --git a/src/testdir/test_debugger.vim b/src/testdir/test_debugger.vim
index fb27007..8c51675 100644
--- a/src/testdir/test_debugger.vim
+++ b/src/testdir/test_debugger.vim
@@ -593,6 +593,99 @@
         \ '->0 script ' .. getcwd() .. '/Xtest2.vim',
         \ 'line 1: func DoAThing()'])
 
+  call RunDbgCmd( buf, 'up' )
+  call RunDbgCmd( buf, 'backtrace', [
+        \ '>backtrace',
+        \ '  4 User Autocommands for "TestGlobalFunction"',
+        \ '  3 function GlobalFunction[1]',
+        \ '  2 CallAFunction[1]',
+        \ '->1 SourceAnotherFile[1]',
+        \ '  0 script ' .. getcwd() .. '/Xtest2.vim',
+        \ 'line 1: func DoAThing()' ] )
+
+  call RunDbgCmd( buf, 'up' )
+  call RunDbgCmd( buf, 'backtrace', [
+        \ '>backtrace',
+        \ '  4 User Autocommands for "TestGlobalFunction"',
+        \ '  3 function GlobalFunction[1]',
+        \ '->2 CallAFunction[1]',
+        \ '  1 SourceAnotherFile[1]',
+        \ '  0 script ' .. getcwd() .. '/Xtest2.vim',
+        \ 'line 1: func DoAThing()' ] )
+
+  call RunDbgCmd( buf, 'up' )
+  call RunDbgCmd( buf, 'backtrace', [
+        \ '>backtrace',
+        \ '  4 User Autocommands for "TestGlobalFunction"',
+        \ '->3 function GlobalFunction[1]',
+        \ '  2 CallAFunction[1]',
+        \ '  1 SourceAnotherFile[1]',
+        \ '  0 script ' .. getcwd() .. '/Xtest2.vim',
+        \ 'line 1: func DoAThing()' ] )
+
+  call RunDbgCmd( buf, 'up' )
+  call RunDbgCmd( buf, 'backtrace', [
+        \ '>backtrace',
+        \ '->4 User Autocommands for "TestGlobalFunction"',
+        \ '  3 function GlobalFunction[1]',
+        \ '  2 CallAFunction[1]',
+        \ '  1 SourceAnotherFile[1]',
+        \ '  0 script ' .. getcwd() .. '/Xtest2.vim',
+        \ 'line 1: func DoAThing()' ] )
+
+  call RunDbgCmd( buf, 'up', [ 'frame at highest level: 4' ] )
+  call RunDbgCmd( buf, 'backtrace', [
+        \ '>backtrace',
+        \ '->4 User Autocommands for "TestGlobalFunction"',
+        \ '  3 function GlobalFunction[1]',
+        \ '  2 CallAFunction[1]',
+        \ '  1 SourceAnotherFile[1]',
+        \ '  0 script ' .. getcwd() .. '/Xtest2.vim',
+        \ 'line 1: func DoAThing()' ] )
+
+  call RunDbgCmd( buf, 'down' )
+  call RunDbgCmd( buf, 'backtrace', [
+        \ '>backtrace',
+        \ '  4 User Autocommands for "TestGlobalFunction"',
+        \ '->3 function GlobalFunction[1]',
+        \ '  2 CallAFunction[1]',
+        \ '  1 SourceAnotherFile[1]',
+        \ '  0 script ' .. getcwd() .. '/Xtest2.vim',
+        \ 'line 1: func DoAThing()' ] )
+
+
+  call RunDbgCmd( buf, 'down' )
+  call RunDbgCmd( buf, 'backtrace', [
+        \ '>backtrace',
+        \ '  4 User Autocommands for "TestGlobalFunction"',
+        \ '  3 function GlobalFunction[1]',
+        \ '->2 CallAFunction[1]',
+        \ '  1 SourceAnotherFile[1]',
+        \ '  0 script ' .. getcwd() .. '/Xtest2.vim',
+        \ 'line 1: func DoAThing()' ] )
+
+  call RunDbgCmd( buf, 'down' )
+  call RunDbgCmd( buf, 'backtrace', [
+        \ '>backtrace',
+        \ '  4 User Autocommands for "TestGlobalFunction"',
+        \ '  3 function GlobalFunction[1]',
+        \ '  2 CallAFunction[1]',
+        \ '->1 SourceAnotherFile[1]',
+        \ '  0 script ' .. getcwd() .. '/Xtest2.vim',
+        \ 'line 1: func DoAThing()' ] )
+
+  call RunDbgCmd( buf, 'down' )
+  call RunDbgCmd( buf, 'backtrace', [
+        \ '>backtrace',
+        \ '  4 User Autocommands for "TestGlobalFunction"',
+        \ '  3 function GlobalFunction[1]',
+        \ '  2 CallAFunction[1]',
+        \ '  1 SourceAnotherFile[1]',
+        \ '->0 script ' .. getcwd() .. '/Xtest2.vim',
+        \ 'line 1: func DoAThing()' ] )
+
+  call RunDbgCmd( buf, 'down', [ 'frame is zero' ] )
+
   " step until we have another meaninfgul trace
   call RunDbgCmd(buf, 'step', ['line 5: func File2Function()'])
   call RunDbgCmd(buf, 'step', ['line 9: call File2Function()'])
diff --git a/src/version.c b/src/version.c
index bb1624f..26075ce 100644
--- a/src/version.c
+++ b/src/version.c
@@ -755,6 +755,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1508,
+/**/
     1507,
 /**/
     1506,