kconfig: tests: test randconfig for choice in choice

Commit 3b9a19e0 ("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

+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

scripts/kconfig/tests/rand_nested_choice/__init__.py

+"""
+Set random values recursively in nested choices.
+
+Kconfig can create a choice-in-choice structure by using 'if' statement.
+randconfig should correctly set random choice values.
+
+Related Linux commit: 3b9a19e08960e5cdad5253998637653e592a3c29
+"""
+
+
+def test(conf):
+    for i in range(20):
+        assert conf.randconfig() == 0
+        assert (conf.config_contains('expected_stdout0') or
+                conf.config_contains('expected_stdout1') or
+                conf.config_contains('expected_stdout2'))

scripts/kconfig/tests/rand_nested_choice/expected_stdout0

+CONFIG_A=y
+# CONFIG_B is not set

scripts/kconfig/tests/rand_nested_choice/expected_stdout1

+# CONFIG_A is not set
+CONFIG_B=y
+CONFIG_C=y
+# CONFIG_D is not set

scripts/kconfig/tests/rand_nested_choice/expected_stdout2

+# CONFIG_A is not set
+CONFIG_B=y
+# CONFIG_C is not set
+CONFIG_D=y
+CONFIG_E=y