jest.config.js中缺少设置collectCoverage: true

module.exports = {
  preset: "ts-jest",
  testEnvironment: "node",
  roots: ["../src/tests/"],
  transform: {
    "^.+\\.tsx?$": "ts-jest"
  },
  collectCoverage: true,
  collectCoverageFrom: ["../src/"],
  moduleFileExtensions: ["ts", "js", "json"],
  coverageDirectory: "../coverage"
};

我还使用了更具描述性的collectCoverageFrom：

collectCoverageFrom: [
    '<rootDir>/src/**/*.ts',
    '!<rootDir>/src/**/*.interface.ts',
    '!<rootDir>/src/**/*.mock.ts',
    '!<rootDir>/src/**/*.module.ts',
    '!<rootDir>/src/**/*.spec.ts',
    '!<rootDir>/src/**/*.test.ts',
    '!<rootDir>/src/**/*.d.ts'
],

这样我就排除了一些不想计算覆盖率的文件，比如我的模块、模拟和测试。
我的完整文件与原始的Jest初始化过程和注解。
有关每个配置属性的详细说明，请访问：the Jest documentation

module.exports = {
    // All imported modules in your tests should be mocked automatically
    // automock: false,

    // Stop running tests after the first failure
    // bail: false,

    // Respect "browser" field in package.json when resolving modules
    // browser: false,

    // The directory where Jest should store its cached dependency information
    // cacheDirectory: "C:\\Users\\sscott\\AppData\\Local\\Temp\\jest",

    // Automatically clear mock calls and instances between every test
    // clearMocks: false,

    // Indicates whether the coverage information should be collected while executing the test
    collectCoverage: true,

    // An array of glob patterns indicating a set of files for which coverage information should be collected
    collectCoverageFrom: [
        '<rootDir>/src/**/*.ts',
        '!<rootDir>/src/**/*.mock.ts',
        '!<rootDir>/src/**/*.module.ts',
        '!<rootDir>/src/**/*.spec.ts',
        '!<rootDir>/src/**/*.test.ts',
        '!<rootDir>/src/**/*.d.ts'
    ],
    // The directory where Jest should output its coverage files
    coverageDirectory: "<rootDir>/docs",

    // An array of regexp pattern strings used to skip coverage collection
    coveragePathIgnorePatterns: [
        "\\\\node_modules\\\\"
    ],

    // A list of reporter names that Jest uses when writing coverage reports
    coverageReporters: [
        "lcov",
        "clover",
        "text-summary"
    ],

    // An object that configures minimum threshold enforcement for coverage results
    // coverageThreshold: null,

    // Make calling deprecated APIs throw helpful error messages
    errorOnDeprecated: true,

    // Force coverage collection from ignored files usin a array of glob patterns
    // forceCoverageMatch: [],

    // A path to a module which exports an async function that is triggered once before all test suites
    // globalSetup: null,

    // A path to a module which exports an async function that is triggered once after all test suites
    // globalTeardown: null,

    // A set of global variables that need to be available in all test environments
    globals: {
        "ts-jest": {
            "diagnostics": false,
            "tsConfig": "tsconfig.json"
        }
    },

    // An array of directory names to be searched recursively up from the requiring module's location
    // moduleDirectories: [
    //   "node_modules"
    // ],

    // An array of file extensions your modules use
    moduleFileExtensions: [
        "ts",
        "tsx",
        "js"
    ],

    // A map from regular expressions to module names that allow to stub out resources with a single module
    // moduleNameMapper: {},

    // An array of regexp pattern strings, matched against all module paths before considered 'visible' to the module loader
    // modulePathIgnorePatterns: [],

    // Activates notifications for test results
    // notify: false,

    // An enum that specifies notification mode. Requires { notify: true }
    // notifyMode: "always",

    // A preset that is used as a base for Jest's configuration
    // preset: null,

    // Run tests from one or more projects
    // projects: null,

    // Use this configuration option to add custom reporters to Jest
    // reporters: undefined,

    // Automatically reset mock state between every test
    // resetMocks: false,

    // Reset the module registry before running each individual test
    // resetModules: false,

    // A path to a custom resolver
    // resolver: null,

    // Automatically restore mock state between every test
    // restoreMocks: false,

    // The root directory that Jest should scan for tests and modules within
    // rootDir: null,

    // A list of paths to directories that Jest should use to search for files in
    roots: [
       "<rootDir>/src"
    ],

    // Allows you to use a custom runner instead of Jest's default test runner
    // runner: "jest-runner",

    // The paths to modules that run some code to configure or set up the testing environment before each test
    // setupFiles: [],

    // The path to a module that runs some code to configure or set up the testing framework before each test
    // setupTestFrameworkScriptFile: null,

    // A list of paths to snapshot serializer modules Jest should use for snapshot testing
    // snapshotSerializers: [],

    // The test environment that will be used for testing
    testEnvironment: "node",

    // Options that will be passed to the testEnvironment
    // testEnvironmentOptions: {},

    // Adds a location field to test results
    // testLocationInResults: false,

    // The glob patterns Jest uses to detect test files
    testMatch: [
        "**/*.spec.ts"
    ],

    // An array of regexp pattern strings that are matched against all test paths, matched tests are skipped
    // testPathIgnorePatterns: [
    //   "\\\\node_modules\\\\"
    // ],

    // The regexp pattern Jest uses to detect test files
    // testRegex: "",

    // This option allows the use of a custom results processor
    // testResultsProcessor: null,
    // "testResultsProcessor": "jest-jenkins-reporter",
    
    // This option allows use of a custom test runner
    // testRunner: "jasmine2",

    // This option sets the URL for the jsdom environment. It is reflected in properties such as location.href
    // testURL: "http://localhost",

    // Setting this value to "fake" allows the use of fake timers for functions such as "setTimeout"
    // timers: "real",

    // A map from regular expressions to paths to transformers
    transform: {
        "^.+\\.(ts|tsx)$": "ts-jest"
    },

    // An array of regexp pattern strings that are matched against all source file paths, matched files will skip transformation
    // transformIgnorePatterns: [
    //   "\\\\node_modules\\\\"
    // ],

    // An array of regexp pattern strings that are matched against all modules before the module loader will automatically return a mock for them
    // unmockedModulePathPatterns: undefined,

    // Indicates whether each individual test should be reported during the run
    verbose: false

    // An array of regexp patterns that are matched against all source file paths before re-running tests in watch mode
    // watchPathIgnorePatterns: [],

    // Whether to use watchman for file crawling
    // watchman: true,
};

经过几页纸的大量研究，这对我得到覆盖率报告起到了作用：
将以下行置于脚本下：

"test:coverage": "set CI=true && react-scripts test --coverage",

并且，在package.json文件中添加以下jest配置代码，如下所示：

"jest": {
    "collectCoverageFrom": [
      "**/*.{js,jsx}",
      "!**/node_modules/**",
      "!**/coverage/**",
      "!**/serviceWorker.js",
      "!**/index.js"
    ],
    "coveragePathIgnorePatterns": [
      "/node_modules/",
      "package.json",
      "package-lock.json"
    ]
  }

然后跑

npm run test:coverage

显然，你必须把你的源文件添加到 * roots * 中才能使它工作。
而不是这个：

roots: ["../src/tests/"]

还包括源文件：

roots: ["../src/tests/", "../src/repositories/"]

之后，如果collectCoverageFrom正确，则按预期检测到覆盖率为0%的所有文件。