CODEWITHSUNDEEP
typescriptunit-testingjestjs
Nate Levin
Nate Levin

Reputation: 1118

What is causing Jest to show 75% branch coverage in this code?

I have a file, parsePredicate.ts, which I believe has no branches in it. However, Jest coverage report is saying that it only has 75% branch coverage. Where are the branches?

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:""});
});

When I run jest --coverage I get the following output for my parsePredicate.ts file:

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

As you can see, it says that line #11 is uncovered. However, line 11 is just an export statement:

export default parsePredicate;

The lcov report looks like this: The lcov report Note that nothing changes if I press n or j.

I have been looking into this, and it seems like it may have to do with the esmodule glue code that is generated by Babel, however I am not sure how to go about fixing that.

Please leave a comment if you need any more information. Any help would be greatly appreciated.

Upvotes: 5

Views: 3426

Answers (1)

Nate Levin
Nate Levin

Reputation: 1118

After quite a long time of trying to figure out the problem on and off, I have come up to the following answer.

Basically, in my jest.config.js I was using the v8 coverage provider.

// Indicates which provider should be used to instrument code for coverage
coverageProvider: "v8",

I use node version 12.16.1, so this provider wasn't really great and had many issues.

Changing to the babel provider fixed all the problems I was having, and gave this code 100% branch coverage.

// Indicates which provider should be used to instrument code for coverage
coverageProvider: "babel",

Upvotes: 2

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