INFO Cannot find test class SampleTest skipping for now

I am using SL4A with ACTS (Android Comms Test Suite) for running some simple test case. but i am getting error as

INFO Cannot find test class SampleTest skipping for now.

here is my config class i.e Sample.json

    {   "_description": "This is an example skeleton test configuration file.",
    "testbed":
    [
        {
            "_description": "Sample testbed with no devices",
            "name": "SampleTestBed"
        }
    ],
    "logpath": "/tmp/logs",
    "testpaths": ["../tests/sample"],
    "custom_param1": {"favorite_food": "Icecream!"}
}

and this is my class i.e SampleTest.py

from acts.base_test import BaseTestClass


class SampleTest(BaseTestClass):

    def __init__(self, controllers):
        BaseTestClass.__init__(self, controllers)
        self.tests = (
            "test_make_toast",
        )

        """Tests"""

    def test_make_toast(self):
        for ad in self.android_devices:
            ad.droid.makeToast("Hello World...")
            return True

and this is how i am running ACT, as follows

act.py -c Sample.json -tb SampleTestBed -tc SampleTest:test_make_toast

but i am getting the above error. any help?

it was a simple issue.. I added tag "AndroidDevice": "*" in Configuration file. and issue got resolved.

 {   "_description": "This is an example skeleton test configuration file.",
    "testbed":
    [
        {
            "_description": "Sample testbed with no devices",
            "name": "SampleTestBed"
           "AndroidDevice": "*"

        }
    ],
    "logpath": "/tmp/logs",
    "testpaths": ["../tests/sample"],
    "custom_param1": {"favorite_food": "Icecream!"}
}