diff --git a/tests/artifactcache/cache_size.py b/tests/artifactcache/cache_size.py
new file mode 100644
index 0000000..0d12cda
--- /dev/null
+++ b/tests/artifactcache/cache_size.py
@@ -0,0 +1,62 @@
+import os
+import pytest
+
+from buildstream import _yaml
+from buildstream._artifactcache import CACHE_SIZE_FILE
+
+from tests.testutils import cli, create_element_size
+
+# XXX: Currently lacking:
+#      * A way to check whether it's faster to read cache size on
+#        successive invocations.
+#      * A way to check whether the cache size file has been read.
+
+
+def create_project(project_dir):
+    project_file = os.path.join(project_dir, "project.conf")
+    project_conf = {
+        "name": "test"
+    }
+    _yaml.dump(project_conf, project_file)
+    element_name = "test.bst"
+    create_element_size(element_name, project_dir, ".", [], 1024)
+
+
+def test_cache_size_roundtrip(cli, tmpdir):
+    # Builds (to put files in the cache), then invokes buildstream again
+    # to check nothing breaks
+
+    # Create project
+    project_dir = str(tmpdir)
+    create_project(project_dir)
+
+    # Build, to populate the cache
+    res = cli.run(project=project_dir, args=["build", "test.bst"])
+    res.assert_success()
+
+    # Show, to check that nothing breaks while reading cache size
+    res = cli.run(project=project_dir, args=["show", "test.bst"])
+    res.assert_success()
+
+
+def test_cache_size_write(cli, tmpdir):
+    # Builds (to put files in the cache), then checks a number is
+    # written to the cache size file.
+
+    project_dir = str(tmpdir)
+    create_project(project_dir)
+
+    # Artifact cache must be in a known place
+    artifactdir = os.path.join(project_dir, "artifacts")
+    cli.configure({"artifactdir": artifactdir})
+
+    # Build, to populate the cache
+    res = cli.run(project=project_dir, args=["build", "test.bst"])
+    res.assert_success()
+
+    # Inspect the artifact cache
+    sizefile = os.path.join(artifactdir, CACHE_SIZE_FILE)
+    assert os.path.isfile(sizefile)
+    with open(sizefile, "r") as f:
+        size_data = f.read()
+    size = int(size_data)