Add mock unittest for S3LogStore

Add boto3 to test dependencies

Pipfile

@@ -3,6 +3,7 @@
 # update these accordingly
 
 [dev-packages]
+boto3 = "*"
 pytest=">=4.6"
 wheel="*"
 pytest-cov="*"

dev-requirements.txt

@@ -1,5 +1,6 @@
 # Note that there is also a Pipfile for this project if you are updating this
 # file do not forget to update the Pipfile accordingly
+boto3
 pyyaml
 pytest>=4.6
 wheel

tests/unit/test_logstore.py

@@ -0,0 +1,57 @@
+"""
+Test S3LogStore
+"""
+# botocore includes a stub
+# https://botocore.amazonaws.com/v1/documentation/api/latest/reference/stubber.html
+# but it doesn't work with upload_file so use mock instead
+# https://sgillies.net/2017/10/19/mock-is-magic.html
+from unittest.mock import patch
+from repo2docker import logstore
+
+
+@patch("repo2docker.logstore.boto3")
+def test_s3logstore_upload(boto3):
+    store = logstore.S3LogStore(
+        endpoint="http://localhost:9000",
+        access_key="access",
+        secret_key="secret",
+        bucket="bucket",
+        keyprefix="prefix/",
+        logname="test/build.log",
+    )
+
+    store.write("hello\n")
+    r = store.close()
+
+    boto3.resource.assert_called_with(
+        "s3",
+        config=boto3.session.Config(signature_version="s3v4"),
+        endpoint_url="http://localhost:9000",
+        aws_access_key_id="access",
+        aws_secret_access_key="secret",
+        region_name="",
+    )
+    boto3.resource().Bucket.assert_called_with("bucket")
+    boto3.resource().Bucket().upload_file.assert_called_with(
+        store._logfile.name,
+        "prefix/test/build.log",
+        ExtraArgs={"ContentType": "text/plain", "ACL": "public-read"},
+    )
+
+
+@patch("repo2docker.logstore.boto3")
+def test_s3logstore_empty(boto3):
+    store = logstore.S3LogStore(
+        endpoint="http://localhost:9000",
+        access_key="access",
+        secret_key="secret",
+        bucket="bucket",
+        keyprefix="prefix/",
+        logname="test/build.log",
+    )
+
+    r = store.close()
+
+    assert not boto3.resource.called
+    assert not boto3.resource().Bucket.called
+    assert not boto3.resource().Bucket().upload_file.called