Provide some debug output upon spec filtering

This might be usefull in debugging issues such as #1181 [1], where user
error and terminal unfamiliarity is the actual root cause.

[1] #1181

lib/add-cucumber-preprocessor-plugin.ts

@@ -1,5 +1,7 @@
 import fs from "fs";
 
+import { inspect } from "node:util";
+
 import { IdGenerator, SourceMediaType } from "@cucumber/messages";
 
 import parse from "@cucumber/tag-expressions";
@@ -47,6 +49,8 @@ import { memoize } from "./helpers/memoize";
 
 import { assertNever } from "./helpers/assertions";
 
+import debug from "./helpers/debug";
+
 const resolve = memoize(origResolve);
 
 export type AddOptions = {
@@ -133,6 +137,8 @@ export async function addCucumberPreprocessorPlugin(
   const tags = getTags(config.env);
 
   if (tags !== null && preprocessor.filterSpecs) {
+    debug(`Filtering specs using expression ${inspect(tags)}`);
+
     const node = parse(tags);
 
     const testFiles = getTestFiles(
@@ -176,6 +182,8 @@ export async function addCucumberPreprocessorPlugin(
       );
     });
 
+    debug(`Resolved specs ${inspect(testFiles)}`);
+
     const propertyName = "specPattern" in config ? "specPattern" : "testFiles";
 
     /**