From 9c66839f853251f25c2a57b5a573f9205d877983 Mon Sep 17 00:00:00 2001
From: Wayne Metcalfe <waynemetcalfe@gmail.com>
Date: Thu, 26 Sep 2019 20:20:53 +0100
Subject: [PATCH] feat: implement logs untag_log_group

---
 IMPLEMENTATION_COVERAGE.md   |  2 +-
 moto/logs/models.py          | 10 ++++++++++
 moto/logs/responses.py       |  6 ++++++
 tests/test_logs/test_logs.py | 20 ++++++++++++++++++++
 4 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/IMPLEMENTATION_COVERAGE.md b/IMPLEMENTATION_COVERAGE.md
index 1377c67b..4c775731 100644
--- a/IMPLEMENTATION_COVERAGE.md
+++ b/IMPLEMENTATION_COVERAGE.md
@@ -4092,7 +4092,7 @@
 - [ ] stop_query
 - [X] tag_log_group
 - [ ] test_metric_filter
-- [ ] untag_log_group
+- [X] untag_log_group
 
 ## machinelearning
 0% implemented
diff --git a/moto/logs/models.py b/moto/logs/models.py
index 01738fa3..cc0d21d4 100644
--- a/moto/logs/models.py
+++ b/moto/logs/models.py
@@ -240,6 +240,10 @@ class LogGroup:
         else:
             self.tags = tags
 
+    def untag(self, tags_to_remove):
+        if self.tags:
+            self.tags = {k: v for (k, v) in self.tags.items() if k not in tags_to_remove}
+
 
 class LogsBackend(BaseBackend):
     def __init__(self, region_name):
@@ -343,5 +347,11 @@ class LogsBackend(BaseBackend):
         log_group = self.groups[log_group_name]
         log_group.tag(tags)
 
+    def untag_log_group(self, log_group_name, tags):
+        if log_group_name not in self.groups:
+            raise ResourceNotFoundException()
+        log_group = self.groups[log_group_name]
+        log_group.untag(tags)
+
 
 logs_backends = {region.name: LogsBackend(region.name) for region in boto.logs.regions()}
diff --git a/moto/logs/responses.py b/moto/logs/responses.py
index 0c8750ce..b91662cf 100644
--- a/moto/logs/responses.py
+++ b/moto/logs/responses.py
@@ -147,3 +147,9 @@ class LogsResponse(BaseResponse):
         tags = self._get_param('tags')
         self.logs_backend.tag_log_group(log_group_name, tags)
         return ''
+
+    def untag_log_group(self):
+        log_group_name = self._get_param('logGroupName')
+        tags = self._get_param('tags')
+        self.logs_backend.untag_log_group(log_group_name, tags)
+        return ''
diff --git a/tests/test_logs/test_logs.py b/tests/test_logs/test_logs.py
index fced0336..22e7edee 100644
--- a/tests/test_logs/test_logs.py
+++ b/tests/test_logs/test_logs.py
@@ -267,3 +267,23 @@ def test_tag_log_group():
     assert response['tags'] == tags_with_updated_value
 
     response = conn.delete_log_group(logGroupName=log_group_name)
+
+
+@mock_logs
+def test_untag_log_group():
+    conn = boto3.client('logs', 'us-west-2')
+    log_group_name = 'dummy'
+    response = conn.create_log_group(logGroupName=log_group_name)
+
+    tags = {'tag_key_1': 'tag_value_1', 'tag_key_2': 'tag_value_2'}
+    response = conn.tag_log_group(logGroupName=log_group_name, tags=tags)
+    response = conn.list_tags_log_group(logGroupName=log_group_name)
+    assert response['tags'] == tags
+
+    tags_to_remove = ['tag_key_1']
+    remaining_tags = {'tag_key_2': 'tag_value_2'}
+    response = conn.untag_log_group(logGroupName=log_group_name, tags=tags_to_remove)
+    response = conn.list_tags_log_group(logGroupName=log_group_name)
+    assert response['tags'] == remaining_tags
+
+    response = conn.delete_log_group(logGroupName=log_group_name)