MOCK_VAR_CONST.md

API Summary

When passing a variable pointer to Patch and Mock, xgo will lookup for package level variables and setup trap for accessing to these variables.

Constant can only be patched via PatchByName(pkg,name,replacer).

Limitation

1. Only variables and consts of main module will be available for patching,
2. Constant patching requires go>=1.20.

Examples

Patch on variable

package patch

import (
    "testing"

    "github.com/xhd2015/xgo/runtime/mock"
)

var a int = 123

func TestPatchVarTest(t *testing.T) {
	mock.Patch(&a, func() int {
		return 456
	})
	b := a
	if b != 456 {
		t.Fatalf("expect patched variable a to be %d, actual: %d", 456, b)
	}
}

Check ../test/patch/patch_var_test.go for more cases.

PatchByName on constant

package patch_const

import (
    "testing"
    
    "github.com/xhd2015/xgo/runtime/mock"
)

const N = 50

func TestPatchConst(t *testing.T) {
    mock.PatchByName("github.com/xhd2015/xgo/runtime/test/patch_const", "N", func() int {
        return 5
    })
    b := N*4

    if b != 20 {
        t.Fatalf("expect b to be %d,actual: %d", 20, b)
    }
}

Check ../test/patch_const/patch_const_test.go for more cases.