bootm: Add tests for fixup_silent_linux()

This function currently has no tests. Export it so that we can implement
a simple test on sandbox. Use IS_ENABLED() to remove the unused code,
instead #ifdef.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/test/bootm.c b/test/bootm.c
new file mode 100644
index 0000000..59d16cb
--- /dev/null
+++ b/test/bootm.c
@@ -0,0 +1,59 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Tests for bootm routines
+ *
+ * Copyright 2020 Google LLC
+ */
+
+#include <common.h>
+#include <bootm.h>
+#include <test/suites.h>
+#include <test/test.h>
+#include <test/ut.h>
+
+DECLARE_GLOBAL_DATA_PTR;
+
+#define BOOTM_TEST(_name, _flags)	UNIT_TEST(_name, _flags, bootm_test)
+
+#define CONSOLE_STR	"console=/dev/ttyS0"
+
+/* Test silent processing in the bootargs variable */
+static int bootm_test_silent_var(struct unit_test_state *uts)
+{
+	/* 'silent_linux' not set should do nothing */
+	env_set("silent_linux", NULL);
+	env_set("bootargs", CONSOLE_STR);
+	fixup_silent_linux();
+	ut_asserteq_str(CONSOLE_STR, env_get("bootargs"));
+
+	env_set("bootargs", NULL);
+	fixup_silent_linux();
+	ut_assertnull(env_get("bootargs"));
+
+	ut_assertok(env_set("silent_linux", "no"));
+	env_set("bootargs", CONSOLE_STR);
+	fixup_silent_linux();
+	ut_asserteq_str(CONSOLE_STR, env_get("bootargs"));
+
+	ut_assertok(env_set("silent_linux", "yes"));
+	env_set("bootargs", CONSOLE_STR);
+	fixup_silent_linux();
+	ut_asserteq_str("console=", env_get("bootargs"));
+
+	/* Empty buffer should still add the string */
+	env_set("bootargs", NULL);
+	fixup_silent_linux();
+	ut_asserteq_str("console=", env_get("bootargs"));
+
+	return 0;
+}
+BOOTM_TEST(bootm_test_silent_var, 0);
+
+int do_ut_bootm(struct cmd_tbl *cmdtp, int flag, int argc, char *const argv[])
+{
+	struct unit_test *tests = ll_entry_start(struct unit_test, bootm_test);
+	const int n_ents = ll_entry_count(struct unit_test, bootm_test);
+
+	return cmd_ut_category("bootm", "bootm_test_", tests, n_ents,
+			       argc, argv);
+}