From e20a3d3747157a9c4830cd4454850f19aa2b2819 Mon Sep 17 00:00:00 2001
From: Ade Attwood <adrian.attwood@marketdojo.com>
Date: Tue, 25 Oct 2022 06:42:34 +0100
Subject: [PATCH] feat: add better error message when the `coverageFile` is not
 found

---
 src/index.ts | 26 +++++++++++++++++++++++---
 1 file changed, 23 insertions(+), 3 deletions(-)

diff --git a/src/index.ts b/src/index.ts
index 754ed11..1f7a907 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,5 +1,6 @@
 import yargs from "yargs";
-import type { Options } from "yargs";
+import fs from "fs";
+import type { Options, Arguments } from "yargs";
 import { hideBin } from "yargs/helpers";
 import exec from "./exec";
 
@@ -11,7 +12,7 @@ const parseDiff = require("./diff-parser");
 const parseLcov = require("./lcov-parser");
 
 export const error = (message: string) => {
-  console.error(message);
+  console.error("[ERROR] " + message);
 };
 
 const options: { [key: string]: Options } = {
@@ -22,8 +23,27 @@ const options: { [key: string]: Options } = {
   },
 };
 
+type Argv = Arguments<
+  Partial<{
+    coverageFile: string;
+  }>
+>;
+
+export const validate = async (argv: Argv) => {
+  if (!fs.existsSync(argv.coverageFile || "")) {
+    return new Error(
+      `Lcov file must be a valid file '${argv.coverageFile}' provided. ` +
+        `Please ensure you have run tests with coverage enabled.`
+    );
+  }
+};
+
 export const run = async (argv = process.argv) => {
-  const parsed: any = yargs(hideBin(argv)).options(options).argv;
+  const parsed: Argv = await yargs(hideBin(argv)).options(options).argv;
+  const validationError = await validate(parsed);
+  if (validationError instanceof Error) {
+    return error(validationError.message);
+  }
 
   const diffText = await exec(`git diff origin/HEAD...HEAD`);
   if (diffText.code > 0) {