Support generator shrinking

Author: sunesimonsen

documentation/index.md

@@ -10,19 +10,24 @@ repository: https://github.com/unexpectedjs/unexpected-check
 
 <img alt="Checkmate!" src="./unexpected-check.jpg" style="display: block; max-width: 100%">
 
-This plugin tries to bring property testing to the
+This plugin tries to bring generative testing (aka property testing) to the
 [unexpected](http://unexpected.js.org) assertion library. The idea is that it
 should be possible to mix property based testing and normal unit-tests using the
 same tool chain.
 
-This project is still in it early days and features such as failure shrinking
-and asynchronous testing are missing. It is currently not possible to configure
-the number of iterations the tests should be executes either
+If the generators you supply supports shrinking by providing a `shrink` function
+on the generator function, unexpected-check will try to shrink the error space
+as much as possible and therefore provide much more precise error cases.
+
+This project is still in it early days and asynchronous testing are missing. It
+is currently not possible to configure the number of iterations the tests should
+be executed either.
 
 I recommend using the plugin together with
-[chance-generators](https://github.com/sunesimonsen/change-generators), but it
-is not a requirement. You can uses any function that produces a random output
-when called as generators.
+[chance-generators](https://github.com/sunesimonsen/change-generators) as it
+provides a huge range of generators and supports shrinking, but it is not a
+requirement. You can uses any function that produces a random output when called
+as generators.
 
 ## Usage
 
@@ -59,18 +64,16 @@ But that assumption as actually not true as the build in sort functions is based
 on converting items to strings and comparing them. So you will get the following error:
 
 ```output
-Ran 23 iterations and found 20 errors
+Ran 44 iterations and found 20 errors
 counterexample:
 
-  Generated input: [ -19, -2, -16 ]
+  Generated input: [ 18, 4 ]
 
-  expected [ -16, -19, -2 ]
-  first item to be less than or equal to all [ -19, -2, -16 ]
+  expected [ 18, 4 ] first item to be less than or equal to all [ 18, 4 ]
 
   [
-    -19, // should be greater than or equal to -16
-    -2,
-    -16
+    18,
+    4 // should be greater than or equal to 18
   ]
 ```
 

lib/unexpected-check.js

@@ -54,8 +54,8 @@
                 var generators = Array.prototype.slice.call(arguments, 2);
 
                 function createTask() {
-                    var args = generators.map(function (generator) {
-                        return generator();
+                    var args = generators.map(function (g) {
+                        return g();
                     });
 
                     var task = {
@@ -65,6 +65,9 @@
                     try {
                         subject.apply(null, args);
                     } catch (e) {
+                        generators = generators.map(function (g, i) {
+                            return g.shrink ? g.shrink(args[i]) : g;
+                        });
                         task.error = convertToUnexpectedError(e);
                     }
 

package.json

@@ -18,7 +18,7 @@
   "author": "Sune Simonsen",
   "license": "MIT",
   "devDependencies": {
-    "chance-generators": "1.0.1",
+    "chance-generators": "1.1.0",
     "eslint": "1.10.3",
     "eslint-config-onelint": "0.0.2",
     "lodash.escape": "3.1.0",

test/unexpected-check.spec.js

@@ -40,18 +40,16 @@ describe('unexpected-check', function () {
                     .and('last item to be greater than or equal to all', arr);
             }, 'to be valid for all', arrays);
         }, 'to throw',
-               'Ran 23 iterations and found 20 errors\n' +
+               'Ran 44 iterations and found 20 errors\n' +
                'counterexample:\n' +
                '\n' +
-               '  Generated input: [ -19, -2, -16 ]\n' +
+               '  Generated input: [ 18, 4 ]\n' +
                '\n' +
-               '  expected [ -16, -19, -2 ]\n' +
-               '  first item to be less than or equal to all [ -19, -2, -16 ]\n' +
+               '  expected [ 18, 4 ] first item to be less than or equal to all [ 18, 4 ]\n' +
                '\n' +
                '  [\n' +
-               '    -19, // should be greater than or equal to -16\n' +
-               '    -2,\n' +
-               '    -16\n' +
+               '    18,\n' +
+               '    4 // should be greater than or equal to 18\n' +
                '  ]');
     });
 
@@ -61,19 +59,15 @@ describe('unexpected-check', function () {
                 expect(arr, 'not to contain', 2);
             }, 'to be valid for all', arrays);
         }, 'to throw',
-               'Ran 52 iterations and found 20 errors\n' +
+               'Ran 25 iterations and found 20 errors\n' +
                'counterexample:\n' +
                '\n' +
-               '  Generated input: [ 2, -17, 9, -13, 7 ]\n' +
+               '  Generated input: [ 2 ]\n' +
                '\n' +
-               '  expected [ 2, -17, 9, -13, 7 ] not to contain 2\n' +
+               '  expected [ 2 ] not to contain 2\n' +
                '\n' +
                '  [\n' +
-               '    2, // should be removed\n' +
-               '    -17,\n' +
-               '    9,\n' +
-               '    -13,\n' +
-               '    7\n' +
+               '    2 // should be removed\n' +
                '  ]');
     });
 
@@ -93,15 +87,37 @@ describe('unexpected-check', function () {
                 expect(items, 'not to contain', i);
             }, 'to be valid for all', arrays, g.integer({ min: -20, max: 20 }));
         }, 'to throw',
-               'Ran 96 iterations and found 20 errors\n' +
+               'Ran 100 iterations and found 18 errors\n' +
                'counterexample:\n' +
                '\n' +
-               '  Generated input: [ -7 ], -7\n' +
+               '  Generated input: [ 3 ], 3\n' +
                '\n' +
-               '  expected [ -7 ] not to contain -7\n' +
+               '  expected [ 3 ] not to contain 3\n' +
                '\n' +
                '  [\n' +
-               '    -7 // should be removed\n' +
+               '    3 // should be removed\n' +
+               '  ]');
+    });
+
+    it('finds needle in a haystack errors', function () {
+        expect(function () {
+            expect(function (items) {
+                expect(items, 'to have items satisfying', function (item, i) {
+                    expect(item, 'not to be', i);
+                });
+            }, 'to be valid for all', arrays);
+        }, 'to throw',
+               'Ran 100 iterations and found 17 errors\n' +
+               'counterexample:\n' +
+               '\n' +
+               '  Generated input: [ -19, 1 ]\n' +
+               '\n' +
+               '  expected [ -19, 1 ]\n' +
+               '  to have items satisfying function (item, i) { expect(item, \'not to be\', i); }\n' +
+               '\n' +
+               '  [\n' +
+               '    -19,\n' +
+               '    1 // should not be 1\n' +
                '  ]');
     });
 });