How to create and use my own golang package locally to get this test to run?

I'm new to golang working through coding exercises and I have all the following files in a directory called leap. I'm using gvm to run the golang executable (version 1.4), using a command such as "go test leap_test.go".

When I do go test leap_test.go I get the following results:

# command-line-arguments
leap_test.go:5:2: open /home/user/go/leap/leap: no such file or directory
FAIL    command-line-arguments [setup failed]

1. How do I include the IsLeap() function so that the tests run correctly.
2. Why is cases_test.go even included? It seems like leap_test.go is all you'd need for tests.

cases_test.go

package leap

// Source: exercism/x-common
// Commit: 945d08e Merge pull request #50 from soniakeys/master

var testCases = []struct {
    year        int
    expected    bool
    description string
}{
    {1996, true, "leap year"},
    {1997, false, "non-leap year"},
    {1998, false, "non-leap even year"},
    {1900, false, "century"},
    {2400, true, "fourth century"},
    {2000, true, "Y2K"},
}

leap_test.go

package leap

import (
    "testing"
    "./leap"
)

var testCases = []struct {
    year        int
    expected    bool
    description string
}{
    {1996, true, "a vanilla leap year"},
    {1997, false, "a normal year"},
    {1900, false, "a century"},
    {2400, true, "an exceptional century"},
}

    func TestLeapYears(t *testing.T) {
        for _, test := range testCases {
            observed := IsLeap(test.year)
            if observed != test.expected {
                t.Fatalf("%v is %s", test.year, test.description)
            }
        }
    }

leap.go

package leap

import(
    "fmt"
)

func IsLeap(year int) bool {
  return true
}