feat(debug): Adding debug log when a get call fails (#3)

* feat(debug_helper): Adding debug helper when a get call fails * fix(review): Few minor changes * moving pretty-format to the dep * fix(review_comments): Making the fixes mentioned in the review comments * Update README.md * Update element-queries.js
testing-library · Apr 10, 2018 · c8069e3 · c8069e3
1 parent d45b449
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diff --git a/README.md b/README.md
@@ -87,6 +87,7 @@ when a real user uses it.
   * [Custom Jest Matchers - Typescript](#custom-jest-matchers---typescript)
 * [`TextMatch`](#textmatch)
 * [`query` APIs](#query-apis)
+* [Debugging](#debugging)
 * [Implementations](#implementations)
 * [FAQ](#faq)
 * [Other Solutions](#other-solutions)
@@ -540,6 +541,42 @@ expect(submitButton).toBeNull() // it doesn't exist
 expect(submitButton).not.toBeInTheDOM()
 ```
 
+## Debugging
+
+When you use any `get` calls in your test cases, the current state of the `container`
+(DOM) gets printed on the console. For example:
+
+```javascript
+// <div>Hello world</div>
+getByText(container, 'Goodbye world') // will fail by throwing error
+```
+
+The above test case will fail, however it prints the state of your DOM under test,
+so you will get to see:
+
+```
+Unable to find an element with the text: Goodbye world. This could be because the text is broken up by multiple elements. In this case, you can provide a function for your text matcher to make your matcher more flexible.
+Here is the state of your container:
+<div>
+  <div>
+    Hello World!
+  </div>
+</div>
+```
+
+Note: Since the DOM size can get really large, you can set the limit of DOM content
+to be printed via environment variable `DEBUG_PRINT_LIMIT`. The default value is
+`7000`. You will see `...` in the console, when the DOM content is stripped off,
+because of the length you have set or due to default size limit. Here's how you
+might increase this limit when running tests:
+
+```
+DEBUG_PRINT_LIMIT=10000 npm test
+```
+
+This works on macOS/linux, you'll need to do something else for windows. If you'd
+like a solution that works for both, see [`cross-env`](https://www.npmjs.com/package/cross-env)
+
 ## Implementations
 
 This library was not built to be used on its own. The original implementation

diff --git a/package.json b/package.json
@@ -35,6 +35,7 @@
   ],
   "dependencies": {
     "jest-matcher-utils": "^22.4.3",
+    "pretty-format": "^22.4.3",
     "mutationobserver-shim": "^0.3.2",
     "wait-for-expect": "^0.4.0"
   },

diff --git a/src/__tests__/__snapshots__/element-queries.js.snap b/src/__tests__/__snapshots__/element-queries.js.snap
@@ -1,15 +1,59 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
-exports[`get throws a useful error message 1`] = `"Unable to find a label with the text of: LucyRicardo"`;
+exports[`get throws a useful error message 1`] = `
+"Unable to find a label with the text of: LucyRicardo 
 
-exports[`get throws a useful error message 2`] = `"Unable to find an element with the placeholder text of: LucyRicardo"`;
+[36m<div>[39m
+  [36m<div />[39m
+[36m</div>[39m"
+`;
 
-exports[`get throws a useful error message 3`] = `"Unable to find an element with the text: LucyRicardo. This could be because the text is broken up by multiple elements. In this case, you can provide a function for your text matcher to make your matcher more flexible."`;
+exports[`get throws a useful error message 2`] = `
+"Unable to find an element with the placeholder text of: LucyRicardo 
 
-exports[`get throws a useful error message 4`] = `"Unable to find an element by: [data-testid=\\"LucyRicardo\\"]"`;
+[36m<div>[39m
+  [36m<div />[39m
+[36m</div>[39m"
+`;
 
-exports[`get throws a useful error message 5`] = `"Unable to find an element with the alt text: LucyRicardo"`;
+exports[`get throws a useful error message 3`] = `
+"Unable to find an element with the text: LucyRicardo. This could be because the text is broken up by multiple elements. In this case, you can provide a function for your text matcher to make your matcher more flexible. 
 
-exports[`label with no form control 1`] = `"Found a label with the text of: alone, however no form control was found associated to that label. Make sure you're using the \\"for\\" attribute or \\"aria-labelledby\\" attribute correctly."`;
+[36m<div>[39m
+  [36m<div />[39m
+[36m</div>[39m"
+`;
 
-exports[`totally empty label 1`] = `"Found a label with the text of: , however no form control was found associated to that label. Make sure you're using the \\"for\\" attribute or \\"aria-labelledby\\" attribute correctly."`;
+exports[`get throws a useful error message 4`] = `
+"Unable to find an element by: [data-testid=\\"LucyRicardo\\"] 
+
+[36m<div>[39m
+  [36m<div />[39m
+[36m</div>[39m"
+`;
+
+exports[`get throws a useful error message 5`] = `
+"Unable to find an element with the alt text: LucyRicardo 
+
+[36m<div>[39m
+  [36m<div />[39m
+[36m</div>[39m"
+`;
+
+exports[`label with no form control 1`] = `
+"Found a label with the text of: alone, however no form control was found associated to that label. Make sure you're using the \\"for\\" attribute or \\"aria-labelledby\\" attribute correctly. 
+
+[36m<div>[39m
+  [36m<label>[39m
+    [0mAll alone[0m
+  [36m</label>[39m
+[36m</div>[39m"
+`;
+
+exports[`totally empty label 1`] = `
+"Found a label with the text of: , however no form control was found associated to that label. Make sure you're using the \\"for\\" attribute or \\"aria-labelledby\\" attribute correctly. 
+
+[36m<div>[39m
+  [36m<label />[39m
+[36m</div>[39m"
+`;
diff --git a/src/__tests__/__snapshots__/wait-for-element.js.snap b/src/__tests__/__snapshots__/wait-for-element.js.snap
@@ -1,48 +1,44 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
-exports[
-  `it returns immediately if the callback returns the value before any mutations 1`
-] = `
+exports[`it returns immediately if the callback returns the value before any mutations 1`] = `
 <div
   data-test-attribute="something changed once"
 >
   <div
     data-testid="initial-element"
   />
 </div>
-`
+`;
 
 exports[`it throws if timeout is exceeded 1`] = `
 Array [
   [Error: Timed out in waitForElement.],
 ]
-`
+`;
 
 exports[`it throws if timeout is exceeded 2`] = `
 <div
   data-test-attribute="something changed twice"
 />
-`
+`;
 
-exports[
-  `it throws the same error that the callback has thrown if timeout is exceeded 1`
-] = `
+exports[`it throws the same error that the callback has thrown if timeout is exceeded 1`] = `
 Array [
-  [Error: Unable to find an element by: [data-testid="test"]],
+  [Error: Unable to find an element by: [data-testid="test"] 
+
+[36m<div[39m
+  [33mdata-test-attribute[39m=[32m"something changed twice"[39m
+[36m/>[39m],
 ]
-`
+`;
 
-exports[
-  `it throws the same error that the callback has thrown if timeout is exceeded 2`
-] = `
+exports[`it throws the same error that the callback has thrown if timeout is exceeded 2`] = `
 <div
   data-test-attribute="something changed twice"
 />
-`
+`;
 
-exports[
-  `it waits for the callback to return a value and only reacts to DOM mutations 1`
-] = `
+exports[`it waits for the callback to return a value and only reacts to DOM mutations 1`] = `
 <div>
   <div
     data-testid="initial-element"
@@ -66,16 +62,16 @@ exports[
     data-testid="the-element-we-are-looking-for"
   />
 </div>
-`
+`;
 
 exports[`it waits for the next DOM mutation with default callback 1`] = `
 <body>
   <div />
 </body>
-`
+`;
 
 exports[`it waits for the next DOM mutation with default callback 2`] = `
 <body>
   <div />
 </body>
-`
+`;
diff --git a/src/__tests__/element-queries.js b/src/__tests__/element-queries.js
@@ -193,4 +193,36 @@ test('using jest helpers to check element class names', () => {
   ).toThrowError()
 })
 
+test('test the debug helper prints the dom state here', () => {
+  const originalDebugPrintLimit = process.env.DEBUG_PRINT_LIMIT
+  const Large = `<div>
+        ${Array.from({length: 7000}, (v, key) => key).map(() => {
+          return `<div data-testid="debugging" data-otherid="debugging">
+                Hello World!
+            </div>`
+        })}
+    </div>`
+
+  const {getByText} = render(Large) // render large DOM which exceeds 7000 limit
+  expect(() => expect(getByText('not present')).toBeInTheDOM()).toThrowError()
+
+  const Hello = `<div data-testid="debugging" data-otherid="debugging">
+        Hello World!
+    </div>`
+  const {getByTestId} = render(Hello)
+  process.env.DEBUG_PRINT_LIMIT = 5 // user should see `...`
+  expect(() => expect(getByTestId('not present')).toBeInTheDOM()).toThrowError(
+    /\.\.\./,
+  )
+
+  const {getByLabelText} = render(Hello)
+  process.env.DEBUG_PRINT_LIMIT = 10000 // user shouldn't see `...`
+  expect(() =>
+    expect(getByLabelText('not present')).toBeInTheDOM(/^((?!\.\.\.).)*$/),
+  ).toThrowError()
+
+  //all good replacing it with old value
+  process.env.DEBUG_PRINT_LIMIT = originalDebugPrintLimit
+})
+
 /* eslint jsx-a11y/label-has-for:0 */
diff --git a/src/queries.js b/src/queries.js
@@ -1,5 +1,8 @@
+import prettyFormat from 'pretty-format'
 import {matches} from './matches'
 
+const {DOMElement, DOMCollection} = prettyFormat.plugins
+
 // Here are the queries for the library.
 // The queries here should only be things that are accessible to both users who are using a screen reader
 // and those who are not using a screen reader (with the exception of the data-testid attribute query).
@@ -78,7 +81,11 @@ function getText(node) {
 function getByTestId(container, id, ...rest) {
   const el = queryByTestId(container, id, ...rest)
   if (!el) {
-    throw new Error(`Unable to find an element by: [data-testid="${id}"]`)
+    throw new Error(
+      `Unable to find an element by: [data-testid="${id}"] \n\n${htmlElementToDisplay(
+        container,
+      )}`,
+    )
   }
   return el
 }
@@ -87,7 +94,9 @@ function getByPlaceholderText(container, text, ...rest) {
   const el = queryByPlaceholderText(container, text, ...rest)
   if (!el) {
     throw new Error(
-      `Unable to find an element with the placeholder text of: ${text}`,
+      `Unable to find an element with the placeholder text of: ${text} \n\n${htmlElementToDisplay(
+        container,
+      )}`,
     )
   }
   return el
@@ -99,10 +108,16 @@ function getByLabelText(container, text, ...rest) {
     const label = queryLabelByText(container, text)
     if (label) {
       throw new Error(
-        `Found a label with the text of: ${text}, however no form control was found associated to that label. Make sure you're using the "for" attribute or "aria-labelledby" attribute correctly.`,
+        `Found a label with the text of: ${text}, however no form control was found associated to that label. Make sure you're using the "for" attribute or "aria-labelledby" attribute correctly. \n\n${htmlElementToDisplay(
+          container,
+        )}`,
       )
     } else {
-      throw new Error(`Unable to find a label with the text of: ${text}`)
+      throw new Error(
+        `Unable to find a label with the text of: ${text} \n\n${htmlElementToDisplay(
+          container,
+        )}`,
+      )
     }
   }
   return el
@@ -112,7 +127,9 @@ function getByText(container, text, ...rest) {
   const el = queryByText(container, text, ...rest)
   if (!el) {
     throw new Error(
-      `Unable to find an element with the text: ${text}. This could be because the text is broken up by multiple elements. In this case, you can provide a function for your text matcher to make your matcher more flexible.`,
+      `Unable to find an element with the text: ${text}. This could be because the text is broken up by multiple elements. In this case, you can provide a function for your text matcher to make your matcher more flexible. \n\n${htmlElementToDisplay(
+        container,
+      )}`,
     )
   }
   return el
@@ -129,11 +146,27 @@ function queryByAltText(container, alt) {
 function getByAltText(container, alt) {
   const el = queryByAltText(container, alt)
   if (!el) {
-    throw new Error(`Unable to find an element with the alt text: ${alt}`)
+    throw new Error(
+      `Unable to find an element with the alt text: ${alt} \n\n${htmlElementToDisplay(
+        container,
+      )}`,
+    )
   }
   return el
 }
 
+function htmlElementToDisplay(htmlElement) {
+  const debugContent = prettyFormat(htmlElement, {
+    plugins: [DOMElement, DOMCollection],
+    printFunctionName: false,
+    highlight: true,
+  })
+  const maxLength = process.env.DEBUG_PRINT_LIMIT || 7000
+  return htmlElement.outerHTML.length > maxLength
+    ? `${debugContent.slice(0, maxLength)}...`
+    : debugContent
+}
+
 export {
   queryByPlaceholderText,
   getByPlaceholderText,