Test for new thread creation

- don't clear the stack trace on continue - track running status
  properly (ish)
- mark threads (running) when the app is executing
- indicate the "current" thread with a different icon

TODO:
- allow user to specify current thread?
- track running status of threads individually?
- allow to pause/continue specific threads?

tests/lib/plugin/shared.vim

@@ -91,3 +91,31 @@ endfunc
 function! ThisTestIsFlaky()
   let g:test_is_flaky = v:true
 endfunction
+
+function! AssertMatchist( expected, actual ) abort
+  let ret = assert_equal( len( a:expected ), len( a:actual ) )
+  let len = min( [ len( a:expected ), len( a:actual ) ] )
+  let idx = 0
+  while idx < len
+    let ret += assert_match( a:expected[ idx ], a:actual[ idx ] )
+    let idx += 1
+  endwhile
+  return ret
+endfunction
+
+
+function! GetBufLine( buf, start, end  = '$' )
+  if type( a:start ) != v:t_string && a:start < 0
+    let start = getbufinfo( a:buf )[ 0 ].linecount + a:start
+  else
+    let start = a:start
+  endif
+
+  if type( a:end ) != v:t_string && a:end < 0
+    let end = getbufinfo( a:buf )[ 0 ].linecount + a:end
+  else
+    let end = a:end
+  endif
+
+  return getbufline( a:buf, start, end )
+endfunction