是什么导致Jest在此代码中显示75％的分支覆盖率？

我有一个文件，parsePredicate.ts我相信其中没有分支。但是，Jest覆盖率报告说它只有75％的分支覆盖率。分公司在哪里？

parsePredicate.ts：

import parseIdentifier from "../parseIdentifier/parseIdentifier";
import parseOperator from "../parseOperator/parseOperator";
import { parseExpression } from "../parseExpression/parseExpression";

const parsePredicate = (str: string)=>{
    let {identifier: left, rest:identRest} = parseIdentifier(str);
    let {operator, rest:opRest} = parseOperator(identRest);
    let {expression: right, rest:exprRest} = parseExpression(opRest);
    return { left: left, operator: operator, right: right, rest: exprRest };
}
export default parsePredicate;

parsePredicate.test.ts：

import parsePredicate from "./parsePredicate";
import parseIdentifier from "../parseIdentifier/parseIdentifier";
import parseOperator from "../parseOperator/parseOperator";
import { parseExpression } from "../parseExpression/parseExpression";

jest.mock("../parseIdentifier/parseIdentifier");
jest.mock("../parseOperator/parseOperator");
jest.mock("../parseExpression/parseExpression");

test("Parsing a predicate with number returns proper values", ()=>{
    // @ts-ignore
    parseIdentifier.mockReturnValueOnce({identifier: "x", rest:" = 1"});
    // @ts-ignore
    parseOperator.mockReturnValueOnce({operator: "=", rest:" 1"});
    // @ts-ignore
    parseExpression.mockReturnValueOnce({expression: "1", rest:""});
    expect(parsePredicate("x = 1")).toStrictEqual({left:"x", operator:"=", right:"1", rest:""});
});
test("Parsing a predicate with math returns proper values", ()=>{
    // @ts-ignore
    parseIdentifier.mockReturnValueOnce({identifier: "x", rest:" = 1 + 1"});
    // @ts-ignore
    parseOperator.mockReturnValueOnce({operator: "=", rest:" 1 + 1"});
    // @ts-ignore
    parseExpression.mockReturnValueOnce({expression: "1 + 1", rest:""});
    expect(parsePredicate("x = 1 + 1")).toStrictEqual({left:"x", operator:"=", right:"1 + 1", rest:""});
});
test("Parsing a predicate with string returns proper values", ()=>{
    // @ts-ignore
    parseIdentifier.mockReturnValueOnce({identifier: "x", rest:" = 'Hello World'"});
    // @ts-ignore
    parseOperator.mockReturnValueOnce({operator: "=", rest:" 'Hello World'"});
    // @ts-ignore
    parseExpression.mockReturnValueOnce({expression: "'Hello World'", rest:""});
    expect(parsePredicate("x = 'Hello World'")).toStrictEqual({left:"x", operator:"=", right:"'Hello World'", rest:""});
});
test("Parsing a predicate with identifier returns proper values", ()=>{
    // @ts-ignore
    parseIdentifier.mockReturnValueOnce({identifier: "x", rest:" = ident"});
    // @ts-ignore
    parseOperator.mockReturnValueOnce({operator: "=", rest:" ident"});
    // @ts-ignore
    parseExpression.mockReturnValueOnce({expression: "ident", rest:""});
    expect(parsePredicate("x = ident")).toStrictEqual({left:"x", operator:"=", right:"ident", rest:""});
});

运行时jest --coverage，我的parsePredicate.ts文件得到以下输出：

---------------------|---------|----------|---------|---------|-------------------
File                 | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
---------------------|---------|----------|---------|---------|-------------------
parsePredicate       |     100 |       75 |     100 |     100 |                   
  parsePredicate.ts  |     100 |       75 |     100 |     100 | 11   

如您所见，它表示未发现第11行。但是，第11行只是一个export语句：

export default parsePredicate;

lcov报告如下所示：请注意，如果按n或j，则没有任何变化。

我一直在寻找到这一点，现在看来似乎可能与由巴贝尔产生esmodule胶水代码来完成，但是我不知道怎么去修复这一点。

如果您需要更多信息，请发表评论。任何帮助将不胜感激。