kconfig: tests: test randconfig for choice in choice

Commit 3b9a19e089 ("kconfig: loop as long as we changed some symbols
in randconfig") fixed randconfig where a choice contains a sub-choice.
Prior to that commit, the sub-choice values were not set.

I am not sure whether this is an intended feature or just something
people discovered works, but it is used in the real world;
drivers/usb/gadget/legacy/Kconfig is source'd in a choice context,
then creates a sub-choice in it.

For the test case in this commit, there are 3 possible results.

Case 1:
  CONFIG_A=y
  # CONFIG_B is not set

Case 2:
  # CONFIG_A is not set
  CONFIG_B=y
  CONFIG_C=y
  # CONFIG_D is not set

Case 3:
  # CONFIG_A is not set
  CONFIG_B=y
  # CONFIG_C is not set
  CONFIG_D=y
  CONFIG_E=y

So, this test iterates several times, and checks if the result is
either of the three.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Ulf Magnusson <ulfalizer@gmail.com>

scripts/kconfig/tests/rand_nested_choice/Kconfig

@@ -0,0 +1,33 @@
+choice
+	prompt "choice"
+
+config A
+	bool "A"
+
+config B
+	bool "B"
+
+if B
+choice
+	prompt "sub choice"
+
+config C
+	bool "C"
+
+config D
+	bool "D"
+
+if D
+choice
+	prompt "subsub choice"
+
+config E
+	bool "E"
+
+endchoice
+endif # D
+
+endchoice
+endif # B
+
+endchoice