fix: fail fast when creating a validator that has no specs.

If an empty array of specs is passed to versionware.NewValidator, all
requests will 404. This is definitely not what callers will expect or
want.

versionware/validator.go

@@ -65,6 +65,9 @@ func today() time.Time {
 // requests according to the given OpenAPI spec versions. For configuration
 // defaults, a nil config may be used.
 func NewValidator(config *ValidatorConfig, docs ...*openapi3.T) (*Validator, error) {
+	if len(docs) == 0 {
+		return nil, fmt.Errorf("no OpenAPI versions provided")
+	}
 	if config == nil {
 		config = &defaultValidatorConfig
 	}

versionware/validator_test.go

@@ -471,9 +471,19 @@ func TestValidator(t *testing.T) {
 
 func TestValidatorConfig(t *testing.T) {
 	c := qt.New(t)
+
+	// No specs provided
 	_, err := versionware.NewValidator(&versionware.ValidatorConfig{ServerURL: "://"})
+	c.Assert(err, qt.ErrorMatches, `no OpenAPI versions provided`)
+
+	// Invalid server URL
+	_, err = versionware.NewValidator(&versionware.ValidatorConfig{ServerURL: "://"}, &openapi3.T{})
 	c.Assert(err, qt.ErrorMatches, `invalid ServerURL: parse "://": missing protocol scheme`)
 
+	// Missing version in OpenAPI spec
+	_, err = versionware.NewValidator(&versionware.ValidatorConfig{ServerURL: "http://example.com"}, &openapi3.T{})
+	c.Assert(err, qt.ErrorMatches, `extension "x-snyk-api-version" not found`)
+
 	docs := make([]*openapi3.T, 2)
 	for i, specStr := range []string{v20210820, v20210916} {
 		doc, err := openapi3.NewLoader().LoadFromData([]byte(specStr))
@@ -482,8 +492,12 @@ func TestValidatorConfig(t *testing.T) {
 		c.Assert(err, qt.IsNil)
 		docs[i] = doc
 	}
+
+	// Invalid server URL
 	_, err = versionware.NewValidator(&versionware.ValidatorConfig{ServerURL: "localhost:8080"}, docs...)
 	c.Assert(err, qt.ErrorMatches, `invalid ServerURL: unsupported scheme "localhost" \(did you forget to specify the scheme://\?\)`)
+
+	// Valid
 	_, err = versionware.NewValidator(&versionware.ValidatorConfig{ServerURL: "http://localhost:8080"}, docs...)
 	c.Assert(err, qt.IsNil)
 	c.Assert(docs[0].Servers[0].URL, qt.Equals, "http://localhost:8080")