tests/lib/fakestore/store: do not hardcode port in fakestore unit tests

The unit tests hardcode the port number, which occasionally seems to be occupied
by something else when running the whole test suite on GH (most likely tests
from another package). Have the port number be selected by the kernel.

Signed-off-by: Maciej Borzecki <[email protected]>

tests/lib/fakestore/store/store.go

@@ -122,6 +122,8 @@ func (s *Store) Start() error {
 		return err
 	}
 
+	s.url = fmt.Sprintf("http://%s", l.Addr())
+
 	go s.srv.Serve(l)
 	return nil
 }

tests/lib/fakestore/store/store_test.go

@@ -22,10 +22,13 @@ package store
 import (
 	"bytes"
 	"encoding/json"
+	"errors"
 	"io"
 	"net/http"
+	"net/url"
 	"os"
 	"path/filepath"
+	"syscall"
 	"testing"
 	"text/template"
 
@@ -47,8 +50,6 @@ type storeTestSuite struct {
 
 var _ = Suite(&storeTestSuite{})
 
-var defaultAddr = "localhost:23321"
-
 func getSha(fn string) (string, uint64) {
 	snapDigest, size, err := asserts.SnapFileSHA3_384(fn)
 	if err != nil {
@@ -61,7 +62,7 @@ func (s *storeTestSuite) SetUpTest(c *C) {
 	topdir := c.MkDir()
 	err := os.Mkdir(filepath.Join(topdir, "asserts"), 0755)
 	c.Assert(err, IsNil)
-	s.store = NewStore(topdir, defaultAddr, false)
+	s.store = NewStore(topdir, "localhost:0", false)
 	err = s.store.Start()
 	c.Assert(err, IsNil)
 
@@ -88,7 +89,22 @@ func (s *storeTestSuite) StorePostJSON(path string, content []byte) (*http.Respo
 }
 
 func (s *storeTestSuite) TestStoreURL(c *C) {
-	c.Assert(s.store.URL(), Equals, "http://"+defaultAddr)
+	u, err := url.Parse(s.store.URL())
+	c.Assert(err, IsNil)
+	c.Check(u.Hostname(), Equals, "127.0.0.1")
+	c.Check(u.Port(), Not(Equals), "")
+}
+
+func (s *storeTestSuite) TestStoreListenAddr(c *C) {
+	u, err := url.Parse(s.store.URL())
+	c.Assert(err, IsNil)
+	// use the same address as the fake store started by the tests so that
+	// this will fail with addr-in-use error
+	topdir := c.MkDir()
+	newstore := NewStore(topdir, u.Host, false)
+	err = newstore.Start()
+	c.Assert(err, NotNil)
+	c.Check(errors.Is(err, syscall.EADDRINUSE), Equals, true)
 }
 
 func (s *storeTestSuite) TestTrivialGetWorks(c *C) {