Allow setting the baseURL of clients

This allows clients to be pointed at local test servers in tests to mock
responses to Airtable API calls.

Signed-off-by: Charlie Egan <charlieegan3@users.noreply.github.com>

client_test.go

@@ -9,6 +9,7 @@ import (
 	"errors"
 	"log"
 	"net/http"
+	"strings"
 	"testing"
 )
 
@@ -35,3 +36,48 @@ func TestClient_do(t *testing.T) {
 		t.Errorf("there should be an error, but was nil")
 	}
 }
+
+func TestClient_SetBaseURL(t *testing.T) {
+	testCases := []struct {
+		description   string
+		url           string
+		expectedError string
+	}{
+		{
+			description: "accepts a valid URL",
+			url:         "http://localhost:3000",
+		},
+		{
+			description: "accepts a valid HTTPS URL",
+			url:         "https://example.com",
+		},
+		{
+			description:   "rejects non http/https scheme url",
+			url:           "ftp://example.com",
+			expectedError: "http or https baseURL must be used",
+		},
+		{
+			description:   "rejects url without scheme",
+			url:           "example.com",
+			expectedError: "scheme of http or https must be specified",
+		},
+	}
+
+	c := testClient(t)
+
+	for _, testCase := range testCases {
+		t.Run(testCase.description, func(t *testing.T) {
+			err := c.SetBaseURL(testCase.url)
+
+			if err != nil {
+				if testCase.expectedError != "" {
+					if !strings.Contains(err.Error(), testCase.expectedError) {
+						t.Fatalf("unexpected error: %s", err)
+					}
+				} else {
+					t.Fatalf("unexpected error: %s", err)
+				}
+			}
+		})
+	}
+}