Allow Addons that affect img tags to be tested

Signed-off-by: Eric Peterson <ericpeterson@spotify.com>

.changeset/techdocs-loose-seal-blooth.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-techdocs-addons-test-utils': patch
+---
+
+Fixed a bug preventing testing of TechDocs Addons whose dom contained `<img />` tags.

plugins/techdocs-addons-test-utils/src/test-utils.tsx

@@ -46,6 +46,7 @@ const techdocsApi = {
 
 const techdocsStorageApi = {
   getApiOrigin: jest.fn(),
+  getBaseUrl: jest.fn(),
   getEntityDocs: jest.fn(),
   syncEntityDocs: jest.fn(),
 };
@@ -180,7 +181,9 @@ export class TechDocsAddonTester {
     techdocsStorageApi.getApiOrigin.mockResolvedValue(
       'https://backstage.example.com/api/techdocs',
     );
-
+    techdocsStorageApi.getBaseUrl.mockResolvedValue(
+      `https://backstage.example.com/api/techdocs/${entityName.namespace}/${entityName.kind}/${entityName.name}/${this.options.path}`,
+    );
     techdocsStorageApi.getEntityDocs.mockResolvedValue(
       renderToStaticMarkup(this.options.dom || defaultDom),
     );