Delete all files in the bucket before starting

spec/bucket_store_integration_spec.rb

@@ -27,6 +27,15 @@
     # This is presented as a single idempotent test as otherwise resetting state between execution
     # makes things very complicated with no huge benefits.
 
+    before do
+      # Even though we make an effort to delete all files in a bucket after we're
+      # done, there may be cases when that doesn't happen (e.g. when the test suite fails),
+      # so we perform an initial cleanup before starting.
+      described_class.for(base_bucket_uri).list.each do |path|
+        described_class.for(path).delete!
+      end
+    end
+
     it "has a consistent interface" do
       # Write 201 files
       file_list = []