Split up [github] testers (#2560)

- Update github contributors badge for `create-service-tester`.

services/github/github-commit-activity.tester.js

@@ -0,0 +1,40 @@
+'use strict'
+
+const Joi = require('joi')
+const { isMetricOverTimePeriod } = require('../test-validators')
+
+const t = (module.exports = require('../create-service-tester')())
+
+t.create('commit activity (1 year)')
+  .get('/y/eslint/eslint.json')
+  .expectJSONTypes(
+    Joi.object().keys({
+      name: 'commit activity',
+      value: isMetricOverTimePeriod,
+    })
+  )
+
+t.create('commit activity (4 weeks)')
+  .get('/4w/eslint/eslint.json')
+  .expectJSONTypes(
+    Joi.object().keys({
+      name: 'commit activity',
+      value: isMetricOverTimePeriod,
+    })
+  )
+
+t.create('commit activity (1 week)')
+  .get('/w/eslint/eslint.json')
+  .expectJSONTypes(
+    Joi.object().keys({
+      name: 'commit activity',
+      value: isMetricOverTimePeriod,
+    })
+  )
+
+t.create('commit activity (repo not found)')
+  .get('/w/badges/helmets.json')
+  .expectJSON({
+    name: 'commit activity',
+    value: 'repo not found',
+  })