Drone + jsonnet apparently requires an extension, so switching back to plain YAML.

.drone.yml

@@ -1,24 +1,40 @@
-local Pipeline(python_version, alpine_version) = {
-    kind: "pipeline",
-    steps: [
-        {
-            name: "build",
-            image: "python:" + python_version + "-alpine" + alpine_version,
-            pull: "always",
-            commands: [
-                "python -m pip install --upgrade pip==19.1.1",
-                "pip install tox==3.10.0",
-                "tox",
-                "apk add --no-cache borgbackup",
-                "tox -e end-to-end"
-            ]
-        }
-    ]
-};
+---
+kind: pipeline
+name: python-3-5-alpine-3-9
 
-[
-    Pipeline("3.5", "3.9"),
-    Pipeline("3.6", "3.9"),
-    Pipeline("3.7", "3.9"),
-    Pipeline("3.7", "3.7")
-]
+steps:
+- name: build
+  image: python:3.5-alpine3.9
+  pull: always
+  commands:
+    - scripts/run-tests
+---
+kind: pipeline
+name: python-3-6-alpine-3-9
+
+steps:
+- name: build
+  image: python:3.6-alpine3.9
+  pull: always
+  commands:
+    - scripts/run-tests
+---
+kind: pipeline
+name: python-3-7-alpine-3-9
+
+steps:
+- name: build
+  image: python:3.7-alpine3.9
+  pull: always
+  commands:
+    - scripts/run-tests
+---
+kind: pipeline
+name: python-3-7-alpine-3-7
+
+steps:
+- name: build
+  image: python:3.7-alpine3.7
+  pull: always
+  commands:
+    - scripts/run-tests

scripts/run-tests

@@ -0,0 +1,14 @@
+#!/bin/bash
+
+# This script is intended to be run from the continuous integration build
+# server, and not on a developer machine. For that, see:
+# https://torsion.org/borgmatic/docs/how-to/develop-on-borgmatic/
+
+set -e
+
+python -m pip install --upgrade pip==19.1.1
+pip install tox==3.10.0
+tox
+apk add --no-cache borgbackup
+tox -e end-to-end
+