kconfig: tests: check unneeded "is not set" with unmet dependency

Commit cb67ab2c ("kconfig: do not write choice values when their
dependency becomes n") fixed a problem where "# CONFIG_... is not set"
for choice values are wrongly written into the .config file when they
are once visible, then become invisible later.

Add a test for this naive case.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Ulf Magnusson <ulfalizer@gmail.com>

scripts/kconfig/tests/no_write_if_dep_unmet/Kconfig

+config A
+	bool "A"
+
+choice
+	prompt "Choice ?"
+	depends on A
+
+config CHOICE_B
+	bool "Choice B"
+
+config CHOICE_C
+	bool "Choice C"
+
+endchoice

scripts/kconfig/tests/no_write_if_dep_unmet/__init__.py

+"""
+Do not write choice values to .config if the dependency is unmet.
+
+"# CONFIG_... is not set" should not be written into the .config file
+for symbols with unmet dependency.
+
+This was not working correctly for choice values because choice needs
+a bit different symbol computation.
+
+This checks that no unneeded "# COFIG_... is not set" is contained in
+the .config file.
+
+Related Linux commit: cb67ab2cd2b8abd9650292c986c79901e3073a59
+"""
+
+
+def test(conf):
+    assert conf.oldaskconfig('config', 'n') == 0
+    assert conf.config_matches('expected_config')

scripts/kconfig/tests/no_write_if_dep_unmet/config

+CONFIG_A=y

scripts/kconfig/tests/no_write_if_dep_unmet/expected_config

+#
+# Automatically generated file; DO NOT EDIT.
+# Linux Kernel Configuration
+#
+# CONFIG_A is not set