format failed results better

LICENSE.md

@@ -0,0 +1,23 @@
+# The MIT License (MIT)
+
+The MIT License (MIT)
+
+Copyright (c) 2021 Sean Sube
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

package.json

@@ -1,4 +1,9 @@
 {
+  "name": "mocha-froth",
+  "version": "0.1.0",
+  "main": "out/src/index.js",
+  "author": "ssube <seansube@gmail.com>",
+  "license": "MIT",
   "devDependencies": {
     "@types/chai-as-promised": "^7.1.4",
     "@types/mocha": "^8.2.3",

src/index.ts

@@ -1,31 +1,19 @@
-import { Arbitrary, check, property } from 'fast-check';
+import { Arbitrary, check, property, RunDetails, Parameters } from 'fast-check';
 
-export type Check<T> = (this: Mocha.Context, t: T) => boolean;
+export type Check<T> = (this: Mocha.Context, val: T) => boolean;
 export type WrappedIt<T> = (name: string, check: Check<T>) => void;
 export type Suite<T> = (it: WrappedIt<T>) => void;
 
-export function over<T>(name: string, strategy: Arbitrary<T>, suite: Suite<T>): void {
+export function over<T>(name: string, strategy: Arbitrary<T>, suite: Suite<T>, parameters?: Parameters<[T]>): void {
   describe(name, () => {
     suite((name, test) => {
       it(name, function (this: Mocha.Context): Promise<void> {
         const ctx = this;
 
         return new Promise((res, rej) => {
-          const result = check(property(strategy, (t) => test.call(ctx, t)));
+          const result = check(property(strategy, (val) => test.call(ctx, val)), parameters);
           if (result.failed) {
-            if (result.counterexample !== null) {
-              const examples = result.counterexample.map(it => {
-                if (typeof it === 'string') {
-                  return `'${it}'`;
-                } else {
-                  return it;
-                }
-              }).join(',');
-              const error = `failed after ${result.numRuns} runs and ${result.numShrinks} shrinks, failing on: ${examples}`;
-              rej(new Error(error));
-            } else {
-              rej(new Error(`failed after ${result.numRuns} runs and ${result.numShrinks} shrinks, without counterexamples`));
-            }
+            rej(new Error(formatDetails(result)));
           } else {
             res();
           }
@@ -34,3 +22,37 @@ export function over<T>(name: string, strategy: Arbitrary<T>, suite: Suite<T>):
     });
   });
 }
+
+export function formatDetails<T>(details: RunDetails<[T]>): string {
+  const prefix = formatPrefix(details);
+  const counts = `${prefix} after ${details.numRuns} runs and ${details.numShrinks} shrinks`;
+
+  if (details.counterexample !== null) {
+    const examples = details.counterexample.map((val) => {
+      if (isString(val)) {
+        return `'${val}'`;
+      } else {
+        return val;
+      }
+    }).join(',');
+    return `${counts}, failing on: ${examples}`;
+  } else {
+    return `${counts}, without counterexamples`;
+  }
+}
+
+export function formatPrefix<T>(details: RunDetails<[T]>): string {
+  if (isString(details.error)) {
+    if (details.error.startsWith('Error:')) {
+      return 'Property failed by throwing an error';
+    }
+
+    return details.error;
+  }
+
+  return 'Property failed without a reason';
+}
+
+export function isString(val: unknown): val is string {
+  return typeof val === 'string';
+}

test/TestOver.ts

@@ -12,12 +12,31 @@ describe('some foo', () => {
     it('should be even', (bar: number) => {
       return bar % 2 === 0;
     });
+
+    it('should not throw', (t: number) => {
+      if (t.toString()[3] === '9') {
+        throw new Error('not a real number!');
+      }
+
+      return true;
+    });
   });
 
   over('some IDs', uuid(), (it) => {
+    beforeEach(() => {
+      console.log('before each ID test');
+    });
+
     it('should be a good one', (id: string) => {
       return id[9] !== 'a';
     });
+
+    it('should be long enough', (id: string) => {
+      return id.length > 2;
+    });
+  }, {
+    examples: [['a']],
+    numRuns: 1_000_000_000,
   });
 
   over('even numbers', integer().filter(n => n % 2 === 0), (it) => {