diff --git a/.github/workflows/deno-ci.yml b/.github/workflows/deno-ci.yml
index 5af8eac..cf145ad 100644
--- a/.github/workflows/deno-ci.yml
+++ b/.github/workflows/deno-ci.yml
@@ -50,6 +50,9 @@ jobs:
     - name: Check entrypoint
       run: time deno cache server.ts
 
+    - name: Run any tests
+      run: time deno test
+
   # Push image to GitHub Packages.
   # See also https://docs.docker.com/docker-hub/builds/
   push:
diff --git a/lib/module-map.ts b/lib/module-map.ts
index 7e0fb7e..4ecaecc 100644
--- a/lib/module-map.ts
+++ b/lib/module-map.ts
@@ -5,21 +5,28 @@ import * as registries from "./module-registries.ts";
 
 export class ModuleMap {
   modules = new Map<string,CodeModule>();
-  mainModule: CodeModule | null = null;
-  mainFile: string | null = null;
+  mainModule: CodeModule;
+  registryOpts: registries.RegistryOpts;
 
   constructor(
     public args: URLSearchParams,
     public redirects: Record<string,string>,
+    public rootNode: DenoModule,
   ) {
-    this.isolateStd = this.args.get('std') === 'isolate';
+    this.registryOpts = {
+      mainModule: rootNode.specifier,
+      isolateStd: this.args.get('std') === 'isolate',
+    }
+
+    this.mainModule = this.grabModFor(
+      rootNode.specifier,
+      rootNode.error ? '#error' : undefined);
   }
-  isolateStd: boolean;
 
   grabModFor(url: string, fragment: string = '') {
     const wireUrl = url.split('#')[0];
     const actualUrl = this.redirects[wireUrl] || wireUrl;
-    const base = registries.determineModuleBase(actualUrl, this.isolateStd);
+    const base = registries.determineModuleBase(actualUrl, this.registryOpts);
     let moduleInfo = this.modules.get(base + fragment);
     if (!moduleInfo) {
       moduleInfo = {
@@ -79,7 +86,7 @@ export class ModuleMap {
     for (const module of this.modules.values()) {
       modules[module.base+module.fragment] = {
         moduleDeps: Array.from(module.deps).map(x => x.base+x.fragment),
-        labelText: registries.determineModuleLabel(module, this.isolateStd),
+        labelText: registries.determineModuleLabel(module, this.registryOpts),
         totalSize: module.totalSize,
         fileCount: module.files.length,
         errors: module.errors,
@@ -96,7 +103,7 @@ export class ModuleMap {
     for (const module of this.modules.values()) {
       // console.log(module.base, Array.from(module.deps.values()).map(x => x.base));
 
-      const labels = registries.determineModuleLabel(module, this.isolateStd);
+      const labels = registries.determineModuleLabel(module, this.registryOpts);
       if (module.errors) {
         labels.unshift(`${module.errors.length} FAILED IMPORTS FROM:`);
         for (const err of module.errors) {
@@ -171,17 +178,13 @@ export class ModuleMap {
 }
 
 export function processDenoInfo(data: DenoInfo, args?: URLSearchParams) {
-  const map = new ModuleMap(args ?? new URLSearchParams, data.redirects);
-
   // TODO: when are there multiple roots?
   const roots = data.roots.map(x => data.redirects[x] || x);
   const rootNode = data.modules.find(x => roots.includes(x.specifier));
   if (!rootNode) throw new Error(
     `I didn't find a root node in the Deno graph! This is a module-visualizer bug.`);
 
-  map.mainModule = map.grabModFor(rootNode.specifier, rootNode.error ? '#error' : undefined);
-  map.mainFile = rootNode.specifier;
-
+  const map = new ModuleMap(args ?? new URLSearchParams, data.redirects, rootNode);
   for (const info of data.modules) {
     map.addFile(info.specifier, info, data);
   }
diff --git a/lib/module-registries.ts b/lib/module-registries.ts
index 7561d80..ef30b94 100644
--- a/lib/module-registries.ts
+++ b/lib/module-registries.ts
@@ -1,16 +1,21 @@
 import type { CodeModule } from "./types.ts";
 
-export function determineModuleBase(fullUrl: string, isolateStd: boolean): string {
+export interface RegistryOpts {
+  mainModule: string;
+  isolateStd?: boolean;
+};
+
+export function determineModuleBase(fullUrl: string, opts: RegistryOpts): string {
   const url = new URL(fullUrl);
   const parts = fullUrl.split('/');
   if (url.protocol === 'file:') return 'file://';
   if (url.protocol !== 'https:') return fullUrl;
   switch (url.host) {
     case 'deno.land':
-      if (parts[3].startsWith('std') && !isolateStd) return parts.slice(0, 4).join('/');
+      if (parts[3].startsWith('std') && !opts.isolateStd) return parts.slice(0, 4).join('/');
       return parts.slice(0, 5).join('/');
     case 'cdn.deno.land':
-      if (parts[3] === 'std' && isolateStd) return parts.slice(0, 8).join('/');
+      if (parts[3] === 'std' && opts.isolateStd) return parts.slice(0, 8).join('/');
       return parts.slice(0, 6).join('/');
     case 'crux.land':
       if (parts.length == 4) return `${url.origin}/${parts[3]}`;
@@ -75,14 +80,14 @@ export function determineModuleBase(fullUrl: string, isolateStd: boolean): strin
   return fullUrl;
 }
 
-export function determineModuleLabel(module: CodeModule, isolateStd: boolean): string[] {
+export function determineModuleLabel(module: CodeModule, opts: RegistryOpts): string[] {
   const url = new URL(module.base);
   const parts = module.base.split('/');
   if (url.protocol !== 'https:') return [module.base];
   switch (url.host) {
     case 'deno.land': {
       let extra = new Array<string>();
-      if (parts[3].startsWith('std') && !isolateStd) {
+      if (parts[3].startsWith('std') && !opts.isolateStd) {
         const folders = new Set(module.files.map(x => x.url.split('/')[4]));
         extra = Array.from(folders).map(x => `    • /${x}`);
       }
@@ -90,7 +95,7 @@ export function determineModuleLabel(module: CodeModule, isolateStd: boolean): s
     }
     case 'cdn.deno.land': {
       let extra = new Array<string>();
-      if (parts[3] === 'std' && !isolateStd) {
+      if (parts[3] === 'std' && !opts.isolateStd) {
         const folders = new Set(module.files.map(x => x.url.split('/')[7]));
         extra = Array.from(folders).map(x => `    • /${x}`);
       }
diff --git a/lib/module-registries_test.ts b/lib/module-registries_test.ts
index 3de98a1..b1a510b 100644
--- a/lib/module-registries_test.ts
+++ b/lib/module-registries_test.ts
@@ -3,14 +3,15 @@ import { assertEquals } from "https://deno.land/std@0.115.0/testing/asserts.ts";
 
 Deno.test('gist', () => {
   const gistBase = 'https://gist.githubusercontent.com/danopia/d8b92fdbaa146133dac74a248e62d761/raw/bf5074703f24fee4c2f08577908115f2a6ffff6a';
-  const gistUrl = `${gistBase}/repro.ts`;
+  const mainModule = `${gistBase}/repro.ts`;
+
+  assertEquals(determineModuleBase(mainModule, { mainModule }), gistBase);
 
-  assertEquals(determineModuleBase(gistUrl, false), gistBase);
   assertEquals(determineModuleLabel({
     base: gistBase, fragment: '',
     deps: new Set(), depsUnversioned: new Set(),
     files: [], totalSize: 0,
-  }, false), [
+  }, { mainModule }), [
     "gist: danopia/d8b92fdbaa146133dac74a248e62d761",
     "  @ bf5074703f24fee4c2f08577908115f2a6ffff6a",
   ]);