feat: new --ouputDiffLines cli flag (#1446)

* docs: add documentation for `--outputTruncateLength` cli flag

* feat: add `--outputDiffLines` cli flag

Use this flag in order to control how many lines are printed,
on each diff.

docs/config/index.md

@@ -237,6 +237,21 @@ Custom reporters for output. Reporters can be [a Reporter instance](https://gith
   - `'json'` -  give a simple JSON summary
   - path of a custom reporter (e.g. `'./path/to/reporter.ts'`, `'@scope/reporter'`)
 
+### outputTruncateLength
+
+- **Type:** `number`
+- **Default:** `80`
+
+Truncate output diff lines up to `80` number of characters. You may wish to tune this,
+depending on you terminal window width.
+
+### outputDiffLines
+
+- **Type:** `number`
+- **Default:** `15`
+
+Limit number of output diff lines up to `15`.
+
 ### outputFile
 
 - **Type:** `string | Record<string, string>`

docs/guide/cli.md

@@ -54,6 +54,8 @@ vitest related /src/index.ts /src/hello-world.js
 | `--silent` | Silent console output from tests |
 | `--isolate` | Isolate environment for each test file (default: `true`) |
 | `--reporter <name>` | Select reporter: `default`, `verbose`, `dot`, `junit`, `json`, or a path to a custom reporter |
+| `--outputTruncateLength <length>` | Truncate output diff lines up to `<length>` number of characters. |
+| `--outputDiffLines <lines>` | Limit number of output diff lines up to `<lines>`. |
 | `--outputFile <filename/-s>` | Write test results to a file when the `--reporter=json` or `--reporter=junit` option is also specified <br /> Via [cac's dot notation] you can specify individual outputs for multiple reporters |
 | `--coverage` | Use c8 for coverage |
 | `--run` | Do not watch |

packages/vitest/src/node/cli.ts

@@ -22,7 +22,8 @@ cli
   .option('--silent', 'silent console output from tests')
   .option('--isolate', 'isolate environment for each test file (default: true)')
   .option('--reporter <name>', 'reporter')
-  .option('--outputTruncateLength <length>', 'diff output length')
+  .option('--outputTruncateLength <length>', 'diff output length (default: 80)')
+  .option('--outputDiffLines <lines>', 'number of diff output lines (default: 15)')
   .option('--outputFile <filename/-s>', 'write test results to a file when the --reporter=json or --reporter=junit option is also specified, use cac\'s dot notation for individual outputs of mutliple reporters')
   .option('--coverage', 'use c8 for coverage')
   .option('--run', 'do not watch')

packages/vitest/src/node/diff.ts

@@ -8,6 +8,7 @@ export function formatLine(line: string, outputTruncateLength?: number) {
 
 export interface DiffOptions {
   outputTruncateLength?: number
+  outputDiffLines?: number
   showLegend?: boolean
 }
 
@@ -24,10 +25,10 @@ export function unifiedDiff(actual: string, expected: string, options: DiffOptio
   if (actual === expected)
     return ''
 
-  const { outputTruncateLength, showLegend = true } = options
+  const { outputTruncateLength, outputDiffLines, showLegend = true } = options
 
   const indent = '  '
-  const diffLimit = 15
+  const diffLimit = outputDiffLines || 15
 
   const counts = {
     '+': 0,

packages/vitest/src/node/error.ts

@@ -8,7 +8,7 @@ import { interpretSourcePos, lineSplitRE, parseStacktrace, posToNumber } from '.
 import { F_POINTER } from '../utils/figures'
 import { stringify } from '../integrations/chai/jest-matcher-utils'
 import type { Vitest } from './core'
-import { unifiedDiff } from './diff'
+import { type DiffOptions, unifiedDiff } from './diff'
 import { divider } from './reporters/renderers/utils'
 
 export function fileFromParsedStack(stack: ParsedStack) {
@@ -62,8 +62,12 @@ export async function printError(error: unknown, ctx: Vitest, options: PrintErro
 
   handleImportOutsideModuleError(e.stack || e.stackStr || '', ctx)
 
-  if (e.showDiff)
-    displayDiff(stringify(e.actual), stringify(e.expected), ctx.console, ctx.config.outputTruncateLength)
+  if (e.showDiff) {
+    displayDiff(stringify(e.actual), stringify(e.expected), ctx.console, {
+      outputTruncateLength: ctx.config.outputTruncateLength,
+      outputDiffLines: ctx.config.outputDiffLines,
+    })
+  }
 }
 
 function printErrorType(type: string, ctx: Vitest) {
@@ -135,8 +139,8 @@ function handleImportOutsideModuleError(stack: string, ctx: Vitest) {
 }\n`)))
 }
 
-function displayDiff(actual: string, expected: string, console: Console, outputTruncateLength?: number) {
-  console.error(c.gray(unifiedDiff(actual, expected, { outputTruncateLength })) + '\n')
+function displayDiff(actual: string, expected: string, console: Console, options?: Omit<DiffOptions, 'showLegend'>) {
+  console.error(c.gray(unifiedDiff(actual, expected, options)) + '\n')
 }
 
 function printErrorMessage(error: ErrorWithDiff, console: Console) {

packages/vitest/src/types/config.ts

@@ -141,6 +141,11 @@ export interface InlineConfig {
    */
   outputTruncateLength?: number
 
+  /**
+   * number of diff output lines
+   */
+  outputDiffLines?: number
+
   /**
    * Write test results to a file when the --reporter=json` or `--reporter=junit` option is also specified.
    * Also definable individually per reporter by using an object instead.