Improve readability of power monitoring code and add additional

tools/telemetry/telemetry/internal/platform/power_monitor/android_fuelgauge_power_monitor_unittest.py

Index: tools/telemetry/telemetry/internal/platform/power_monitor/android_fuelgauge_power_monitor_unittest.py
diff --git a/tools/telemetry/telemetry/internal/platform/power_monitor/android_fuelgauge_power_monitor_unittest.py b/tools/telemetry/telemetry/internal/platform/power_monitor/android_fuelgauge_power_monitor_unittest.py
index f049f0e3acf7c33383bfa37ad70ba326147255dd..a40bae8b8e8c34dca841e10b5159e7101c505be0 100644
--- a/tools/telemetry/telemetry/internal/platform/power_monitor/android_fuelgauge_power_monitor_unittest.py
+++ b/tools/telemetry/telemetry/internal/platform/power_monitor/android_fuelgauge_power_monitor_unittest.py
@@ -6,6 +6,7 @@ import unittest
 
 from telemetry.internal.platform.power_monitor import (
     android_fuelgauge_power_monitor)
+from telemetry.internal.platform.power_monitor import pm_mock
 
 
 class FuelGaugePowerMonitorMonitorTest(unittest.TestCase):
@@ -19,6 +20,32 @@ class FuelGaugePowerMonitorMonitorTest(unittest.TestCase):
     self.assertEqual(
         results.get('fuel_gauge_energy_consumption_mwh'), 400)
 
+  def testMonitorCycle(self):
+    battery = pm_mock.MockBattery(None, voltage=5.0, fuelgauge=[5.e6, 3.e6])
+    backend = pm_mock.MockPlatformBackend()
+    pm = android_fuelgauge_power_monitor.FuelGaugePowerMonitor(battery, backend)
+    pm.StartMonitoringPower(None)
+    results = pm.StopMonitoringPower()
+    self.assertEqual(results['identifier'], 'fuel_gauge')
+    self.assertAlmostEqual(results['fuel_gauge_energy_consumption_mwh'], 10)
+
+  def testDoubleStop(self):
+    battery = pm_mock.MockBattery(None, voltage=5.0, fuelgauge=[5.e6, 3.e6])
+    backend = pm_mock.MockPlatformBackend()
+    pm = android_fuelgauge_power_monitor.FuelGaugePowerMonitor(battery, backend)
+    pm.StartMonitoringPower(None)
+    pm.StopMonitoringPower()
+    with self.assertRaises(AssertionError):
+      pm.StopMonitoringPower()
+
+  def testDoubleStart(self):
+    battery = pm_mock.MockBattery(None, voltage=5.0, fuelgauge=[5.e6, 3.e6])
+    backend = pm_mock.MockPlatformBackend()
+    pm = android_fuelgauge_power_monitor.FuelGaugePowerMonitor(battery, backend)
+    pm.StartMonitoringPower(None)
+    with self.assertRaises(AssertionError):
+      pm.StartMonitoringPower(None)
+
 
 if __name__ == '__main__':
   unittest.main()