[jest-each] Add each array validation check (#7033)

CHANGELOG.md

@@ -9,6 +9,7 @@
 
 ### Fixes
 
+- `[jest-each]` Add each array validation check ([#7033](https://github.com/facebook/jest/pull/7033))
 - `[jest-haste-map]` [**BREAKING**] Replace internal data structures to improve performance ([#6960](https://github.com/facebook/jest/pull/6960))
 - `[jest-haste-map]` Do not visit again files with the same sha-1 ([#6990](https://github.com/facebook/jest/pull/6990))
 - `[jest-jasmine2]` Fix memory leak in Error objects hold by the framework ([#6965](https://github.com/facebook/jest/pull/6965))

packages/jest-each/src/__tests__/__snapshots__/array.test.js.snap

@@ -0,0 +1,57 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`jest-each .describe throws an error when not called with an array 1`] = `
+"\`.each\` must be called with an Array or Tagged Template String.
+
+Instead was called with: undefined
+"
+`;
+
+exports[`jest-each .describe.only throws an error when not called with an array 1`] = `
+"\`.each\` must be called with an Array or Tagged Template String.
+
+Instead was called with: undefined
+"
+`;
+
+exports[`jest-each .fdescribe throws an error when not called with an array 1`] = `
+"\`.each\` must be called with an Array or Tagged Template String.
+
+Instead was called with: undefined
+"
+`;
+
+exports[`jest-each .fit throws an error when not called with an array 1`] = `
+"\`.each\` must be called with an Array or Tagged Template String.
+
+Instead was called with: undefined
+"
+`;
+
+exports[`jest-each .it throws an error when not called with an array 1`] = `
+"\`.each\` must be called with an Array or Tagged Template String.
+
+Instead was called with: undefined
+"
+`;
+
+exports[`jest-each .it.only throws an error when not called with an array 1`] = `
+"\`.each\` must be called with an Array or Tagged Template String.
+
+Instead was called with: undefined
+"
+`;
+
+exports[`jest-each .test throws an error when not called with an array 1`] = `
+"\`.each\` must be called with an Array or Tagged Template String.
+
+Instead was called with: undefined
+"
+`;
+
+exports[`jest-each .test.only throws an error when not called with an array 1`] = `
+"\`.each\` must be called with an Array or Tagged Template String.
+
+Instead was called with: undefined
+"
+`;

packages/jest-each/src/__tests__/array.test.js

@@ -47,6 +47,19 @@ describe('jest-each', () => {
     ['describe', 'only'],
   ].forEach(keyPath => {
     describe(`.${keyPath.join('.')}`, () => {
+      test('throws an error when not called with an array', () => {
+        const globalTestMocks = getGlobalTestMocks();
+        const eachObject = each.withGlobal(globalTestMocks)(undefined);
+        const testFunction = get(eachObject, keyPath);
+
+        testFunction('expected string', noop);
+        const globalMock = get(globalTestMocks, keyPath);
+
+        expect(() =>
+          globalMock.mock.calls[0][1](),
+        ).toThrowErrorMatchingSnapshot();
+      });
+
       test('calls global with given title', () => {
         const globalTestMocks = getGlobalTestMocks();
         const eachObject = each.withGlobal(globalTestMocks)([[]]);

packages/jest-each/src/bind.js

@@ -23,12 +23,35 @@ const SUPPORTED_PLACEHOLDERS = /%[sdifjoOp%]/g;
 const PRETTY_PLACEHOLDER = '%p';
 const INDEX_PLACEHOLDER = '%#';
 
+const errorWithStack = (message, callsite) => {
+  const error = new Error(message);
+  if (Error.captureStackTrace) {
+    Error.captureStackTrace(error, callsite);
+  }
+  return error;
+};
+
 export default (cb: Function, supportsDone: boolean = true) => (...args: any) =>
   function eachBind(title: string, test: Function, timeout: number): void {
     if (args.length === 1) {
-      const table: Table = args[0].every(Array.isArray)
-        ? args[0]
-        : args[0].map(entry => [entry]);
+      const [tableArg] = args;
+
+      if (!Array.isArray(tableArg)) {
+        const error = errorWithStack(
+          '`.each` must be called with an Array or Tagged Template String.\n\n' +
+            `Instead was called with: ${pretty(tableArg, {
+              maxDepth: 1,
+              min: true,
+            })}\n`,
+          eachBind,
+        );
+        return cb(title, () => {
+          throw error;
+        });
+      }
+      const table: Table = tableArg.every(Array.isArray)
+        ? tableArg
+        : tableArg.map(entry => [entry]);
       return table.forEach((row, i) =>
         cb(
           arrayFormat(title, i, ...row),
@@ -47,7 +70,7 @@ export default (cb: Function, supportsDone: boolean = true) => (...args: any) =>
     const missingData = data.length % keys.length;
 
     if (missingData > 0) {
-      const error = new Error(
+      const error = errorWithStack(
         'Not enough arguments supplied for given headings:\n' +
           EXPECTED_COLOR(keys.join(' | ')) +
           '\n\n' +
@@ -58,12 +81,9 @@ export default (cb: Function, supportsDone: boolean = true) => (...args: any) =>
             'argument',
             missingData,
           )}`,
+        eachBind,
       );
 
-      if (Error.captureStackTrace) {
-        Error.captureStackTrace(error, eachBind);
-      }
-
       return cb(title, () => {
         throw error;
       });