27126: a few more contexts where executing empty lists gives status zero

Test/A01grammar.ztst

@@ -27,6 +27,18 @@
   $nonexistent_variable
 0:Executing command that evaluates to empty resets status
 
+  false
+  sleep 1 &
+  print $?
+  # a tidy test is a happy test
+  wait $!
+0:Starting background command resets status
+>0
+
+  false
+  . /dev/null
+0:Sourcing empty file resets status
+
   fn() { local foo; read foo; print $foo; }
   coproc fn
   print -p coproc test output
@@ -531,3 +543,13 @@
   . ./bad_syntax
 126: Attempt to "." file with bad syntax.
 ?./bad_syntax:2: parse error near `\n'
+
+  echo 'false' >dot_false
+  . ./dot_false
+  print $?
+  echo 'true' >dot_true
+  . ./dot_true
+  print $?
+0:Last status of successfully executed "." file is retained
+>1
+>0

Test/C04funcdef.ztst

@@ -1,5 +1,20 @@
 %test
 
+  fn1() { return 1; }
+  fn2() {
+      fn1
+      print $?
+      return 2
+  }
+  fn2
+2:Basic status returns from functions
+>1
+
+  fnz() { }
+  false
+  fnz
+0:Empty function body resets status
+
   function f$$ () {
     print regress expansion of function names
   }

Test/D08cmdsubst.ztst

@@ -89,3 +89,7 @@
   X=$(exit 2) $(exit 0) || print $?
 0:variable assignments processed after other substitutions
 >2
+
+ false
+ ``
+0:Empty command substitution resets status