Added tests for eslint ☀️

jest.config.ts

@@ -8,7 +8,7 @@ const config: JestConfigWithTsJest = {
     'src/**/*.ts',
     // TODO: Write tests for these files when they are less likely to change
     '!src/index.ts',
-    '!src/linters/(eslint|index|stylelint).ts',
+    '!src/linters/(index|stylelint).ts',
   ],
   coverageDirectory: 'coverage',
   coverageThreshold: {

src/linters/__tests__/eslint.spec.ts

@@ -0,0 +1,198 @@
+import { ESLint } from 'eslint'
+
+import colourLog from '@Utils/colourLog'
+
+import eslintLib from '../eslint'
+
+jest.mock('eslint')
+jest.mock('@Utils/colourLog')
+
+describe('eslint', () => {
+
+  jest.spyOn(colourLog, 'error').mockImplementation(() => {})
+
+  const testFiles = ['index.ts']
+  const lintFilesMock = ESLint.prototype.lintFiles as jest.Mock
+
+  it('creates a new ESLint instance', async () => {
+    lintFilesMock.mockImplementationOnce(() => [])
+
+    await eslintLib.lintFiles(testFiles)
+
+    expect(ESLint).toHaveBeenCalledTimes(1)
+    expect(ESLint).toHaveBeenCalledWith({
+      cache: false,
+      fix: false,
+    })
+  })
+
+  it('calls eslint with the files', async () => {
+    lintFilesMock.mockImplementationOnce(() => [])
+
+    await eslintLib.lintFiles(testFiles)
+
+    expect(ESLint.prototype.lintFiles).toHaveBeenCalledTimes(1)
+    expect(ESLint.prototype.lintFiles).toHaveBeenCalledWith(testFiles)
+  })
+
+  it('exists the process when eslint throws an error', async () => {
+    expect.assertions(2)
+
+    const error = new Error('Test error') as any
+
+    lintFilesMock.mockImplementationOnce(() => {
+      throw error
+    })
+
+    try {
+      await eslintLib.lintFiles(testFiles)
+    } catch {
+      expect(colourLog.error).toHaveBeenCalledOnceWith('An error occurred while running eslint', error)
+      expect(process.exit).toHaveBeenCalledWith(1)
+    }
+  })
+
+  it('resolves with results and a summary when eslint successfully lints (no errors)', async () => {
+    const lintResults: Array<ESLint.LintResult> = [{
+      errorCount: 0,
+      fatalErrorCount: 0,
+      filePath: `${process.cwd()}/index.ts`,
+      fixableErrorCount: 0,
+      fixableWarningCount: 0,
+      messages: [],
+      suppressedMessages: [],
+      usedDeprecatedRules: [],
+      warningCount: 0,
+    }]
+
+    lintFilesMock.mockImplementationOnce(() => lintResults)
+
+    expect(await eslintLib.lintFiles(testFiles)).toStrictEqual({
+      results: {},
+      summary: {
+        deprecatedRules: [],
+        errorCount: 0,
+        fileCount: 1,
+        fixableErrorCount: 0,
+        fixableWarningCount: 0,
+        linter: 'ESLint',
+        warningCount: 0,
+      },
+    })
+  })
+
+  it('resolves with results and a summary when eslint successfully lints (with errors, warnings, and deprecations)', async () => {
+    const lintResults: Array<ESLint.LintResult> = [{
+      errorCount: 0,
+      fatalErrorCount: 0,
+      filePath: `${process.cwd()}/constants.ts`,
+      fixableErrorCount: 0,
+      fixableWarningCount: 0,
+      messages: [],
+      suppressedMessages: [],
+      usedDeprecatedRules: [],
+      warningCount: 0,
+    }, {
+      errorCount: 4,
+      fatalErrorCount: 0,
+      filePath: `${process.cwd()}/index.ts`,
+      fixableErrorCount: 3,
+      fixableWarningCount: 1,
+      messages: [{
+        column: 1,
+        line: 1,
+        message: 'Normal rule error',
+        ruleId: 'normal-error',
+        severity: 2,
+      }, {
+        column: 1,
+        line: 2,
+        message: 'Normal rule warning',
+        ruleId: 'normal-warning',
+        severity: 1,
+      }, {
+        column: 1,
+        line: 3,
+        message: 'Error with trailing whitespace ',
+        ruleId: 'spaced-error',
+        severity: 2,
+      }],
+      suppressedMessages: [],
+      usedDeprecatedRules: [{
+        ruleId: 'deprecated-rule-1',
+        replacedBy: ['new-rule-1'],
+      }],
+      warningCount: 2,
+    }, {
+      errorCount: 1,
+      fatalErrorCount: 0,
+      filePath: `${process.cwd()}/utils.ts`,
+      fixableErrorCount: 0,
+      fixableWarningCount: 0,
+      // @ts-expect-error - line is required, but for ignored files it is not provided
+      messages: [{
+        column: 1,
+        message: 'Test core error',
+        ruleId: null,
+        severity: 1,
+      }],
+      suppressedMessages: [],
+      usedDeprecatedRules: [{
+        ruleId: 'deprecated-rule-1',
+        replacedBy: ['new-rule-1'],
+      }, {
+        ruleId: 'deprecated-rule-2',
+        replacedBy: ['new-rule-2'],
+      }],
+      warningCount: 0,
+    }]
+
+    const commonResult = {
+      messageTheme: expect.any(Function),
+      positionTheme: expect.any(Function),
+      ruleTheme: expect.any(Function),
+    }
+
+    lintFilesMock.mockImplementationOnce(() => lintResults)
+
+    expect(await eslintLib.lintFiles(testFiles)).toStrictEqual({
+      results: {
+        'index.ts': [{
+          ...commonResult,
+          position: '1:1',
+          message: 'Normal rule error',
+          rule: 'normal-error',
+          severity: 'X',
+        }, {
+          ...commonResult,
+          position: '2:1',
+          message: 'Normal rule warning',
+          rule: 'normal-warning',
+          severity: '!',
+        }, {
+          ...commonResult,
+          position: '3:1',
+          message: 'Error with trailing whitespace',
+          rule: 'spaced-error',
+          severity: 'X',
+        }],
+        'utils.ts': [{
+          ...commonResult,
+          position: '1:1',
+          message: 'Test core error',
+          rule: 'core-error',
+          severity: 'X',
+        }],
+      },
+      summary: {
+        deprecatedRules: ['deprecated-rule-1', 'deprecated-rule-2'],
+        errorCount: 5,
+        fileCount: 3,
+        fixableErrorCount: 3,
+        fixableWarningCount: 1,
+        linter: 'ESLint',
+        warningCount: 2,
+      },
+    })
+  })
+})