diff --git a/tools/releasetools/add_img_to_target_files.py b/tools/releasetools/add_img_to_target_files.py
index a37de66..bbb5abd 100755
--- a/tools/releasetools/add_img_to_target_files.py
+++ b/tools/releasetools/add_img_to_target_files.py
@@ -96,7 +96,16 @@
 
 
 def GetCareMap(which, imgname):
-  """Generates the care_map for the given partition."""
+  """Returns the care_map string for the given partition.
+
+  Args:
+    which: The partition name, must be listed in PARTITIONS_WITH_CARE_MAP.
+    imgname: The filename of the image.
+
+  Returns:
+    (which, care_map_ranges): care_map_ranges is the raw string of the care_map
+    RangeSet.
+  """
   assert which in PARTITIONS_WITH_CARE_MAP
 
   simg = sparse_img.SparseImage(imgname)
diff --git a/tools/releasetools/test_add_img_to_target_files.py b/tools/releasetools/test_add_img_to_target_files.py
index e449ca8..9a0f78e 100644
--- a/tools/releasetools/test_add_img_to_target_files.py
+++ b/tools/releasetools/test_add_img_to_target_files.py
@@ -20,7 +20,11 @@
 import zipfile
 
 import common
-from add_img_to_target_files import AddPackRadioImages, AddRadioImagesForAbOta
+import test_utils
+from add_img_to_target_files import (
+    AddCareMapTxtForAbOta, AddPackRadioImages, AddRadioImagesForAbOta,
+    GetCareMap)
+from rangelib import RangeSet
 
 
 OPTIONS = common.OPTIONS
@@ -166,3 +170,170 @@
 
     self.assertRaises(AssertionError, AddPackRadioImages, None,
                       images + ['baz'])
+
+  @staticmethod
+  def _test_AddCareMapTxtForAbOta():
+    """Helper function to set up the test for test_AddCareMapTxtForAbOta()."""
+    OPTIONS.info_dict = {
+        'system_verity_block_device' : '/dev/block/system',
+        'vendor_verity_block_device' : '/dev/block/vendor',
+    }
+
+    # Prepare the META/ folder.
+    meta_path = os.path.join(OPTIONS.input_tmp, 'META')
+    if not os.path.exists(meta_path):
+      os.mkdir(meta_path)
+
+    system_image = test_utils.construct_sparse_image([
+        (0xCAC1, 6),
+        (0xCAC3, 4),
+        (0xCAC1, 6)])
+    vendor_image = test_utils.construct_sparse_image([
+        (0xCAC2, 10)])
+
+    image_paths = {
+        'system' : system_image,
+        'vendor' : vendor_image,
+    }
+    return image_paths
+
+  def test_AddCareMapTxtForAbOta(self):
+    image_paths = self._test_AddCareMapTxtForAbOta()
+
+    AddCareMapTxtForAbOta(None, ['system', 'vendor'], image_paths)
+
+    care_map_file = os.path.join(OPTIONS.input_tmp, 'META', 'care_map.txt')
+    with open(care_map_file, 'r') as verify_fp:
+      care_map = verify_fp.read()
+
+    lines = care_map.split('\n')
+    self.assertEqual(4, len(lines))
+    self.assertEqual('system', lines[0])
+    self.assertEqual(RangeSet("0-5 10-15").to_string_raw(), lines[1])
+    self.assertEqual('vendor', lines[2])
+    self.assertEqual(RangeSet("0-9").to_string_raw(), lines[3])
+
+  def test_AddCareMapTxtForAbOta_withNonCareMapPartitions(self):
+    """Partitions without care_map should be ignored."""
+    image_paths = self._test_AddCareMapTxtForAbOta()
+
+    AddCareMapTxtForAbOta(
+        None, ['boot', 'system', 'vendor', 'vbmeta'], image_paths)
+
+    care_map_file = os.path.join(OPTIONS.input_tmp, 'META', 'care_map.txt')
+    with open(care_map_file, 'r') as verify_fp:
+      care_map = verify_fp.read()
+
+    lines = care_map.split('\n')
+    self.assertEqual(4, len(lines))
+    self.assertEqual('system', lines[0])
+    self.assertEqual(RangeSet("0-5 10-15").to_string_raw(), lines[1])
+    self.assertEqual('vendor', lines[2])
+    self.assertEqual(RangeSet("0-9").to_string_raw(), lines[3])
+
+  def test_AddCareMapTxtForAbOta_withAvb(self):
+    """Tests the case for device using AVB."""
+    image_paths = self._test_AddCareMapTxtForAbOta()
+    OPTIONS.info_dict = {
+        'avb_system_hashtree_enable' : 'true',
+        'avb_vendor_hashtree_enable' : 'true',
+    }
+
+    AddCareMapTxtForAbOta(None, ['system', 'vendor'], image_paths)
+
+    care_map_file = os.path.join(OPTIONS.input_tmp, 'META', 'care_map.txt')
+    with open(care_map_file, 'r') as verify_fp:
+      care_map = verify_fp.read()
+
+    lines = care_map.split('\n')
+    self.assertEqual(4, len(lines))
+    self.assertEqual('system', lines[0])
+    self.assertEqual(RangeSet("0-5 10-15").to_string_raw(), lines[1])
+    self.assertEqual('vendor', lines[2])
+    self.assertEqual(RangeSet("0-9").to_string_raw(), lines[3])
+
+  def test_AddCareMapTxtForAbOta_verityNotEnabled(self):
+    """No care_map.txt should be generated if verity not enabled."""
+    image_paths = self._test_AddCareMapTxtForAbOta()
+    OPTIONS.info_dict = {}
+    AddCareMapTxtForAbOta(None, ['system', 'vendor'], image_paths)
+
+    care_map_file = os.path.join(OPTIONS.input_tmp, 'META', 'care_map.txt')
+    self.assertFalse(os.path.exists(care_map_file))
+
+  def test_AddCareMapTxtForAbOta_missingImageFile(self):
+    """Missing image file should be considered fatal."""
+    image_paths = self._test_AddCareMapTxtForAbOta()
+    image_paths['vendor'] = ''
+    self.assertRaises(AssertionError, AddCareMapTxtForAbOta, None,
+                      ['system', 'vendor'], image_paths)
+
+  def test_AddCareMapTxtForAbOta_zipOutput(self):
+    """Tests the case with ZIP output."""
+    image_paths = self._test_AddCareMapTxtForAbOta()
+
+    output_file = common.MakeTempFile(suffix='.zip')
+    with zipfile.ZipFile(output_file, 'w') as output_zip:
+      AddCareMapTxtForAbOta(output_zip, ['system', 'vendor'], image_paths)
+
+    with zipfile.ZipFile(output_file, 'r') as verify_zip:
+      care_map = verify_zip.read('META/care_map.txt').decode('ascii')
+
+    lines = care_map.split('\n')
+    self.assertEqual(4, len(lines))
+    self.assertEqual('system', lines[0])
+    self.assertEqual(RangeSet("0-5 10-15").to_string_raw(), lines[1])
+    self.assertEqual('vendor', lines[2])
+    self.assertEqual(RangeSet("0-9").to_string_raw(), lines[3])
+
+  def test_AddCareMapTxtForAbOta_zipOutput_careMapEntryExists(self):
+    """Tests the case with ZIP output which already has care_map entry."""
+    image_paths = self._test_AddCareMapTxtForAbOta()
+
+    output_file = common.MakeTempFile(suffix='.zip')
+    with zipfile.ZipFile(output_file, 'w') as output_zip:
+      # Create an existing META/care_map.txt entry.
+      common.ZipWriteStr(output_zip, 'META/care_map.txt', 'dummy care_map.txt')
+
+      # Request to add META/care_map.txt again.
+      AddCareMapTxtForAbOta(output_zip, ['system', 'vendor'], image_paths)
+
+    # The one under OPTIONS.input_tmp must have been replaced.
+    care_map_file = os.path.join(OPTIONS.input_tmp, 'META', 'care_map.txt')
+    with open(care_map_file, 'r') as verify_fp:
+      care_map = verify_fp.read()
+
+    lines = care_map.split('\n')
+    self.assertEqual(4, len(lines))
+    self.assertEqual('system', lines[0])
+    self.assertEqual(RangeSet("0-5 10-15").to_string_raw(), lines[1])
+    self.assertEqual('vendor', lines[2])
+    self.assertEqual(RangeSet("0-9").to_string_raw(), lines[3])
+
+    # The existing entry should be scheduled to be replaced.
+    self.assertIn('META/care_map.txt', OPTIONS.replace_updated_files_list)
+
+  def test_GetCareMap(self):
+    sparse_image = test_utils.construct_sparse_image([
+        (0xCAC1, 6),
+        (0xCAC3, 4),
+        (0xCAC1, 6)])
+    OPTIONS.info_dict = {
+        'system_adjusted_partition_size' : 12,
+    }
+    name, care_map = GetCareMap('system', sparse_image)
+    self.assertEqual('system', name)
+    self.assertEqual(RangeSet("0-5 10-12").to_string_raw(), care_map)
+
+  def test_GetCareMap_invalidPartition(self):
+    self.assertRaises(AssertionError, GetCareMap, 'oem', None)
+
+  def test_GetCareMap_invalidAdjustedPartitionSize(self):
+    sparse_image = test_utils.construct_sparse_image([
+        (0xCAC1, 6),
+        (0xCAC3, 4),
+        (0xCAC1, 6)])
+    OPTIONS.info_dict = {
+        'system_adjusted_partition_size' : -12,
+    }
+    self.assertRaises(AssertionError, GetCareMap, 'system', sparse_image)