How Can I Achieve 100% Test Coverage for Go's os.Exit() Scenarios with Goveralls?

Testing Go os.Exit Scenarios with Coverage Information (coveralls.io/Goveralls)

The ability to test scenarios involving os.Exit() is crucial in Go development. However, os.Exit() is difficult to intercept directly. A common method involves reinvoking the binary and checking the exit status.

This approach faces limitations, primarily the lack of coverage information with Goveralls and the potential fragility of rerunning the test binary.

Achieving 100% Coverage

To address these challenges, consider a refactoring of the testing code:

package foo

import (
    "fmt"
    "io"
    "log"
    "os"
    "testing"
)

var (
    osExit = os.Exit
    logFatalf = log.Fatalf
)

// Tester interface for mocking os.Exit() and log.Fatalf()
type Tester interface {
    Fatal(string, ...interface{})
    Exit(int)
}

type realTester struct{}

func (r realTester) Fatal(s string, v ...interface{}) {
    log.Fatalf(s, v...)
}

func (r realTester) Exit(code int) {
    os.Exit(code)
}

func Crasher() {
    fmt.Print("Going down in flames!")
    logFatalf("Exiting with code: %d", 1)
}

// TestCrasher simulates os.Exit() and log.Fatalf()
func TestCrasher(t *testing.T) {
    tests := []struct {
        name string
        f    func(t *testing.T, original Tester, tester *mockTester)
    }{
        {"Test os.Exit()", func(t *testing.T, orig, test *mockTester) {
            orig.Exit(1)
            if test.exitCode != 1 {
                t.Errorf("expected exit code 1, got %d", test.exitCode)
            }
        }},
        {"Test log.Fatalf()", func(t *testing.T, orig, test *mockTester) {
            orig.Fatalf("Exiting after a test failure")
            if test.format != "Exiting after a test failure" {
                t.Errorf("expected format \"Exiting after a test failure\", got %s", test.format)
            }
        }},
    }

    for _, test := range tests {
        t.Run(test.name, func(t *testing.T) {
            var orig Tester = realTester{}
            var mr mockTester

            test.f(t, orig, &mr)

            mr.Verify()
        })
    }
}

// Mock tester simulates os.Exit() and log.Fatalf()
type mockTester struct {
    format    string
    values    []interface{}
    exitCode  int
    exitCalls int
}

func (m *mockTester) Fatal(s string, v ...interface{}) {
    m.format = s
    m.values = v
    m.exit()
}

func (m *mockTester) Exit(code int) {
    m.exitCode = code
    m.exit()
}

func (m *mockTester) exit() {
    m.exitCalls++
}

// Verify checks that mockTester was called appropriately
func (m *mockTester) Verify() {
    if m.exitCalls != 1 {
        panic("expected 1 call to Exit() or Fatal(), got %d", m.exitCalls)
    }
}

This approach refactors the testing code into a reusable Tester interface, allowing for mocking of both os.Exit() and log.Fatalf(). By explicitly calling Exit() or Fatal() in the mock object and simulating the behavior, you can achieve 100% coverage for these scenarios.

The above is the detailed content of How Can I Achieve 100% Test Coverage for Go's os.Exit() Scenarios with Goveralls?. For more information, please follow other related articles on the PHP Chinese website!