Add test for github.com special handling

cli/command/image/build_test.go

@@ -68,3 +68,37 @@ func TestRunBuildDockerfileFromStdinWithCompress(t *testing.T) {
 	sort.Strings(actual)
 	assert.Equal(t, []string{dockerfileName, ".dockerignore", "foo"}, actual)
 }
+
+// TestRunBuildFromLocalGitHubDirNonExistingRepo tests that build contexts
+// starting with `github.com/` are special-cased, and the build command attempts
+// to clone the remote repo.
+func TestRunBuildFromGitHubSpecialCase(t *testing.T) {
+	cmd := NewBuildCommand(&command.DockerCli{})
+	cmd.SetArgs([]string{"github.com/docker/no-such-repository"})
+	cmd.SetOutput(ioutil.Discard)
+	err := cmd.Execute()
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "unable to prepare context: unable to 'git clone'")
+}
+
+// TestRunBuildFromLocalGitHubDirNonExistingRepo tests that a local directory
+// starting with `github.com` takes precedence over the `github.com` special
+// case.
+func TestRunBuildFromLocalGitHubDir(t *testing.T) {
+	tmpDir, err := ioutil.TempDir("", "docker-build-from-local-dir-")
+	require.NoError(t, err)
+	defer os.RemoveAll(tmpDir)
+
+	buildDir := filepath.Join(tmpDir, "github.com", "docker", "no-such-repository")
+	err = os.MkdirAll(buildDir, 0777)
+	require.NoError(t, err)
+	err = ioutil.WriteFile(filepath.Join(buildDir, "Dockerfile"), []byte("FROM busybox\n"), 0644)
+	require.NoError(t, err)
+
+	client := test.NewFakeCli(&fakeClient{})
+	cmd := NewBuildCommand(client)
+	cmd.SetArgs([]string{buildDir})
+	cmd.SetOutput(ioutil.Discard)
+	err = cmd.Execute()
+	require.NoError(t, err)
+}