spec: introduce getBaseRatios to retrieve ratios from spawn-ed process

src/spec/index.ts

@@ -186,6 +186,13 @@ export const baseRatioFromPath = async (path: string) => {
     return extractBaseRatio(result);
 };
 
+export async function getBaseRatios<T extends ChildProcessByStdio<null | Writable, Readable, Readable>>(proc: T) {
+    const specResultCSVs = (await watchSPEC(proc)).outputFiles["CSV"];
+    assert(specResultCSVs !== undefined && specResultCSVs.length === 1);
+    const specCSV = await fs.promises.readFile(specResultCSVs[0], "utf-8");
+    return extractBaseRatio(parseSPECCSVResultsTable(specCSV));
+}
+
 export interface ParsedResult {
     [key: string]: SPECResultsTable;
 }