Core: Add automatic labels in test.each() for primitive values in arrays

Cherry-picked from bf42d2b (3.0.0-dev).

> Fixes #1733.

src/test.js

@@ -997,10 +997,56 @@ function makeEachTestName (testName, argument) {
   return `${testName} [${argument}]`;
 }
 
+// Characters to avoid in test names especially CLI/AP output:
+// * x00-1F: e.g. NULL, backspace (\b), line breaks (\r\n), ESC.
+// * x74: DEL.
+// * xA0: non-breaking space.
+//
+// See https://en.wikipedia.org/wiki/ASCII#Character_order
+//
+// eslint-disable-next-line no-control-regex
+const rNonObviousStr = /[\x00-\x1F\x7F\xA0]/;
 function runEach (data, eachFn) {
   if (Array.isArray(data)) {
     for (let i = 0; i < data.length; i++) {
-      eachFn(data[i], i);
+      const value = data[i];
+
+      // Create automatic labels for primitive data in arrays passed to test.each().
+      // We want to avoid the default "example [0], example [1]" where possible since
+      // these are not self-explanatory in results, and are also tedious to locate
+      // the source of since the numerical key of an array isn't literally in the
+      // code (you have to count).
+      //
+      // Design requirements:
+      // * Unique. Each label must be unique and correspond 1:1 with a data value.
+      //   This way each test name will hash to a unique testId with Rerun link,
+      //   without having to rely on Test class enforcing uniqueness with invisible
+      //   space hack.
+      // * Unambigious. While technical uniqueness is a hard requirement above,
+      //   we also want the labels to be obvious and unambiguous to humans.
+      //   For example, abbrebating "foobar" and "foobaz" to "f" and "fo" is
+      //   technically unique, but ambigious to humans which one is which.
+      // * Short and readable. Where possible we omit the array index numbers
+      //   so that in most cases, the value is simply shown as-is.
+      //   We prefer "example [foo], example [bar]"
+      //   over "example [0: foo], example [2: bar]".
+      //   This also has the benefit of being stable and robust against e.g.
+      //   re-ordering data or adding new items during development, without
+      //   invalidating a previous filter or rerun link immediately.
+      const valueType = typeof value;
+      let testKey = i;
+      if (valueType === 'string' && value.length <= 40 && !rNonObviousStr.test(value) && !/\s*\d+: /.test(value)) {
+        testKey = value;
+      } else if (valueType === 'string' || valueType === 'number' || valueType === 'boolean' || valueType === 'undefined' || value === null) {
+        const valueForName = String(value);
+        if (!rNonObviousStr.test(valueForName)) {
+          testKey = i + ': ' + (valueForName.length <= 30
+            ? valueForName
+            : valueForName.slice(0, 29) + '…'
+          );
+        }
+      }
+      eachFn(value, testKey);
     }
   } else if (typeof data === 'object' && data !== null) {
     for (let key in data) {

test/cli/fixtures/each-array-labels.js

@@ -0,0 +1,44 @@
+// Automatic labels for test.each() array data where possible
+// https://github.com/qunitjs/qunit/issues/1733
+
+QUnit.test.each('array of arrays', [[1, 2, 3], [1, 1, 2]], function (assert, _data) {
+  assert.true(true);
+});
+
+QUnit.test.each('array of simple strings', [
+  'foo',
+  'x'.repeat(40),
+  '$',
+  'http://example.org',
+  ' ',
+  ''
+], function (assert, _data) {
+  assert.true(true);
+});
+
+QUnit.test.each('array of mixed', [
+  undefined,
+  null,
+  false,
+  true,
+  0,
+  1,
+  -10,
+  10 / 3,
+  10e42,
+  Infinity,
+  NaN,
+  [],
+  {},
+  '999: example',
+  'simple string',
+  '\b',
+  '\n',
+  'y'.repeat(100)
+], function (assert, _value) {
+  assert.true(true);
+});
+
+QUnit.test.each('keyed objects', { caseFoo: [1, 2, 3], caseBar: [1, 1, 2] }, function (assert, _data) {
+  assert.true(true);
+});

test/cli/fixtures/each-array-labels.tap.txt

@@ -0,0 +1,36 @@
+# command: ["qunit", "each-array-labels.js"]
+
+TAP version 13
+ok 1 array of arrays [0]
+ok 2 array of arrays [1]
+ok 3 array of simple strings [foo]
+ok 4 array of simple strings [xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx]
+ok 5 array of simple strings [$]
+ok 6 array of simple strings [http://example.org]
+ok 7 array of simple strings [ ]
+ok 8 array of simple strings []
+ok 9 array of mixed [0: undefined]
+ok 10 array of mixed [1: null]
+ok 11 array of mixed [2: false]
+ok 12 array of mixed [3: true]
+ok 13 array of mixed [4: 0]
+ok 14 array of mixed [5: 1]
+ok 15 array of mixed [6: -10]
+ok 16 array of mixed [7: 3.3333333333333335]
+ok 17 array of mixed [8: 1e+43]
+ok 18 array of mixed [9: Infinity]
+ok 19 array of mixed [10: NaN]
+ok 20 array of mixed [11]
+ok 21 array of mixed [12]
+ok 22 array of mixed [13: 999: example]
+ok 23 array of mixed [simple string]
+ok 24 array of mixed [15]
+ok 25 array of mixed [16]
+ok 26 array of mixed [17: yyyyyyyyyyyyyyyyyyyyyyyyyyyyy…]
+ok 27 keyed objects [caseFoo]
+ok 28 keyed objects [caseBar]
+1..28
+# pass 28
+# skip 0
+# todo 0
+# fail 0

test/cli/fixtures/test-if.tap.txt

@@ -5,10 +5,10 @@ TAP version 13
 ok 1 # SKIP skip me
 ok 2 keep me
 ok 3 regular
-ok 4 # SKIP skip dataset [0]
-ok 5 # SKIP skip dataset [1]
-ok 6 keep dataset [0]
-ok 7 keep dataset [1]
+ok 4 # SKIP skip dataset [a]
+ok 5 # SKIP skip dataset [b]
+ok 6 keep dataset [a]
+ok 7 keep dataset [b]
 ok 8 # SKIP skip group > skipper
 ok 9 keep group > keeper
 1..9

test/main/promise.js

@@ -248,21 +248,21 @@ QUnit.module('Support for Promise', function () {
     }
   });
 
-  QUnit.test.each('fulfilled Promise', [1], function (assert, _data) {
+  QUnit.test.each('fulfilled Promise', ['x'], function (assert, _data) {
     assert.expect(1);
 
     // Adds 1 assertion
     return createMockPromise(assert);
   });
 
-  QUnit.test.each('rejected Promise with Error', [1], function (assert, _data) {
+  QUnit.test.each('rejected Promise with Error', ['x'], function (assert, _data) {
     assert.expect(2);
 
     this.pushFailure = assert.test.pushFailure;
     assert.test.pushFailure = function (message) {
       assert.strictEqual(
         message,
-        'Promise rejected during "rejected Promise with Error [0]": this is an error'
+        'Promise rejected during "rejected Promise with Error [x]": this is an error'
       );
     };