cmd/pkgserver: move StreamReporter display() to Reporter interface

cmd/pkgserver/ui/static/test.ts

@@ -7,12 +7,12 @@ export interface TestResult {
 // Reporting
 
 export interface Reporter {
-    update(path: string[], result: TestResult);
+    update(path: string[], result: TestResult): void;
-    finalize();
+    finalize(): void;
 }
 
 export interface Stream {
-    writeln(s: string);
+    writeln(s: string): void;
 }
 
 export class StreamReporter implements Reporter {
@@ -29,6 +29,7 @@ export class StreamReporter implements Reporter {
     }
 
     update(path: string[], result: TestResult) {
+        if (path.length === 0) throw new RangeError("path is empty");
         const pathStr = path.join(' ❯ ');
         if (result.success) {
             this.counts.successes++;
@@ -77,6 +78,7 @@ export class StreamReporter implements Reporter {
 
 export class DOMReporter implements Reporter {
     update(path: string[], result: TestResult) {
+        if (path.length === 0) throw new RangeError("path is empty");
         const counter = document.getElementById(result.success ? 'successes' : 'failures');
         counter.innerText = (Number(counter.innerText) + 1).toString();
         let parent = document.getElementById('root');