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+In test, we set a test-specific "HOME", which cause OS X keychain look for the
+default keychain of a "different" user. If the default keychain does not exist,
+all subsequent calls to OS X keychain will fail. User interaction (such as
+specifying password) is required to create a keychain. However, user interaction
+is not feasible in automated tests.
+
+This problem is caused by the OS X system assumption that one user must have a
+login keychain, which is also the user's default keychain, because a user
+account is always created with a login keychain as default. Thus OS X system
+infers a user according to the HOME env, and did not expect user to change the
+HOME env in normal use.