Improve error output for missing or malformed '-database' and '-source' parameters

migrate.go

@@ -82,13 +82,13 @@ type Migrate struct {
 func New(sourceUrl, databaseUrl string) (*Migrate, error) {
 	m := newCommon()
 
-	sourceName, err := schemeFromUrl(sourceUrl)
+	sourceName, err := sourceSchemeFromUrl(sourceUrl)
 	if err != nil {
 		return nil, err
 	}
 	m.sourceName = sourceName
 
-	databaseName, err := schemeFromUrl(databaseUrl)
+	databaseName, err := databaseSchemeFromUrl(databaseUrl)
 	if err != nil {
 		return nil, err
 	}

util.go

@@ -1,6 +1,7 @@
 package migrate
 
 import (
+	"errors"
 	"fmt"
 	nurl "net/url"
 	"strings"
@@ -43,15 +44,35 @@ func suint(n int) uint {
 	return uint(n)
 }
 
-var errNoScheme = fmt.Errorf("no scheme")
+var errNoScheme = errors.New("no scheme")
+var errEmptyURL = errors.New("URL cannot be empty")
+
+func sourceSchemeFromUrl(url string) (string, error) {
+	u, err := schemeFromUrl(url)
+	if err != nil {
+		return "", fmt.Errorf("source: %v", err)
+	}
+	return u, nil
+}
+
+func databaseSchemeFromUrl(url string) (string, error) {
+	u, err := schemeFromUrl(url)
+	if err != nil {
+		return "", fmt.Errorf("database: %v", err)
+	}
+	return u, nil
+}
 
 // schemeFromUrl returns the scheme from a URL string
 func schemeFromUrl(url string) (string, error) {
+	if url == "" {
+		return "", errEmptyURL
+	}
+
 	u, err := nurl.Parse(url)
 	if err != nil {
 		return "", err
 	}
-
 	if len(u.Scheme) == 0 {
 		return "", errNoScheme
 	}

util_test.go

@@ -1,6 +1,7 @@
 package migrate
 
 import (
+	"errors"
 	nurl "net/url"
 	"testing"
 )
@@ -30,3 +31,85 @@ func TestFilterCustomQuery(t *testing.T) {
 		t.Fatalf("didn't expect x-custom")
 	}
 }
+
+func TestSourceSchemeFromUrlSuccess(t *testing.T) {
+	urlStr := "protocol://path"
+	expected := "protocol"
+
+	u, err := sourceSchemeFromUrl(urlStr)
+	if err != nil {
+		t.Fatalf("expected no error, but received %q", err)
+	}
+	if u != expected {
+		t.Fatalf("expected %q, but received %q", expected, u)
+	}
+}
+
+func TestSourceSchemeFromUrlFailure(t *testing.T) {
+	cases := []struct {
+		name      string
+		urlStr    string
+		expectErr error
+	}{
+		{
+			name:      "Empty",
+			urlStr:    "",
+			expectErr: errors.New("source: URL cannot be empty"),
+		},
+		{
+			name:      "NoScheme",
+			urlStr:    "hello",
+			expectErr: errors.New("source: no scheme"),
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			_, err := sourceSchemeFromUrl(tc.urlStr)
+			if err.Error() != tc.expectErr.Error() {
+				t.Fatalf("expected %q, but received %q", tc.expectErr, err)
+			}
+		})
+	}
+}
+
+func TestDatabaseSchemeFromUrlSuccess(t *testing.T) {
+	urlStr := "protocol://path"
+	expected := "protocol"
+
+	u, err := databaseSchemeFromUrl(urlStr)
+	if err != nil {
+		t.Fatalf("expected no error, but received %q", err)
+	}
+	if u != expected {
+		t.Fatalf("expected %q, but received %q", expected, u)
+	}
+}
+
+func TestDatabaseSchemeFromUrlFailure(t *testing.T) {
+	cases := []struct {
+		name      string
+		urlStr    string
+		expectErr error
+	}{
+		{
+			name:      "Empty",
+			urlStr:    "",
+			expectErr: errors.New("database: URL cannot be empty"),
+		},
+		{
+			name:      "NoScheme",
+			urlStr:    "hello",
+			expectErr: errors.New("database: no scheme"),
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			_, err := databaseSchemeFromUrl(tc.urlStr)
+			if err.Error() != tc.expectErr.Error() {
+				t.Fatalf("expected %q, but received %q", tc.expectErr, err)
+			}
+		})
+	}
+}