我尝试测试用Go语言编写的代码，但我不断收到此错误，但我不知道为什么

首先，我自己编写了一个名为trace的程序包，它有两个文件，以运行我写到终端的整个程序包：

go test -cover

但是会出现此错误：

--- FAIL: TestNew (0.00s)
    tracer_test.go:19: We haven't written our test yet
FAIL
coverage: 100.0% of statements
exit status 1
FAIL    gizmo/go/src/trace      0.172s

这是跟踪包中两个文件的代码：第一个，tracer.go

package trace

import (
    "io"
    "fmt"
)

//Tracer is the interface that describes an object capable of tracing events throughout code

type Tracer interface {
    Trace(...interface{})
}


type tracer struct {
    out io.Writer
}

func (t *tracer) Trace(a ...interface{}){
    fmt.Fprint(t.out, a...)
    fmt.Fprintln(t.out)
}

func New(w io.Writer) Tracer {
    return &tracer{out: w}
}

第二个，tracer_test.go

package trace

import (
    "testing"
    "bytes"
)

func TestNew(t *testing.T) {
    var buf bytes.Buffer
    tracer := New(&buf)
    if tracer == nil {
        t.Error("Return from New should not be nil")
    } else {
        tracer.Trace("Hello trace package.")
        if buf.String() != "Hello trace package.\n" {
            t.Errorf("Trace should not write '%s'.", buf.String())
        }
    }
    t.Error("We haven't written our test yet")
}

我真的很想有人帮助我，我被困住了。（我不希望测试失败但要通过）。