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// math/math.go
package math

import "errors"

func Divide(a, b float64) (float64, error) {
    if b == 0 {
        return 0, errors.New("division by zero")
    }
    return a / b, nil
}

// math/math_test.go
package math_test

import (
    "math"         // standard library math for comparison
    "testing"

mymath "github.com/example/app/math"
)

func TestDivide(t *testing.T) {
    t.Parallel()

tests := []struct {
        name    string
        a, b    float64
        want    float64
        wantErr bool
    }{
        {"positive", 10, 2, 5, false},
        {"negative divisor", -6, 3, -2, false},
        {"float", 1, 3, 1.0 / 3.0, false},
        {"divide by zero", 5, 0, 0, true},
    }

for _, tc := range tests {
        tc := tc // capture range variable
        t.Run(tc.name, func(t *testing.T) {
            t.Parallel()
            got, err := mymath.Divide(tc.a, tc.b)
            if (err != nil) != tc.wantErr {
                t.Errorf("Divide(%v, %v) error = %v, wantErr %v",
                    tc.a, tc.b, err, tc.wantErr)
                return
            }
            if !tc.wantErr && math.Abs(got-tc.want) > 1e-9 {
                t.Errorf("Divide(%v, %v) = %v, want %v", tc.a, tc.b, got, tc.want)
            }
        })
    }
}