Refactor "init" version parsing, and add unit-test

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

daemon/info_unix_test.go

@@ -0,0 +1,52 @@
+// +build !windows
+
+package daemon
+
+import (
+	"testing"
+
+	"github.com/docker/docker/api/types"
+	"github.com/docker/docker/dockerversion"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestParseInitVersion(t *testing.T) {
+	tests := []struct {
+		version string
+		result  types.Commit
+		invalid bool
+	}{
+		{
+			version: "tini version 0.13.0 - git.949e6fa",
+			result:  types.Commit{ID: "949e6fa", Expected: dockerversion.InitCommitID[0:7]},
+		}, {
+			version: "tini version 0.13.0\n",
+			result:  types.Commit{ID: "v0.13.0", Expected: dockerversion.InitCommitID},
+		}, {
+			version: "tini version 0.13.2",
+			result:  types.Commit{ID: "v0.13.2", Expected: dockerversion.InitCommitID},
+		}, {
+			version: "tini version0.13.2",
+			result:  types.Commit{ID: "N/A", Expected: dockerversion.InitCommitID},
+			invalid: true,
+		}, {
+			version: "",
+			result:  types.Commit{ID: "N/A", Expected: dockerversion.InitCommitID},
+			invalid: true,
+		}, {
+			version: "hello world",
+			result:  types.Commit{ID: "N/A", Expected: dockerversion.InitCommitID},
+			invalid: true,
+		},
+	}
+
+	for _, test := range tests {
+		ver, err := parseInitVersion(string(test.version))
+		if test.invalid {
+			assert.Error(t, err)
+		} else {
+			assert.NoError(t, err)
+		}
+		assert.Equal(t, test.result, ver)
+	}
+}