feat(#21): provide basic verifier client

README.md

@@ -109,6 +109,13 @@ Useful for unit testing.
     mockClient := aurestmock.New(mockResponses, mockErrors)
 ```
 
+#### 1c. Or use verifier (super-basic consumer interaction testing)
+
+This mock client doesn't make actual requests, but instead you set up a list of
+expected interactions.
+
+This allows doing very simple consumer tests, useful mostly for their documentation value.
+
 #### 2. Response recording
 
 If your tests use Option 1a (playback), you should insert a response recorder in your production stack.

implementation/verifier/verifier.go

@@ -0,0 +1,145 @@
+package aurestverifier
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	aurestclientapi "github.com/StephanHCB/go-autumn-restclient/api"
+	"io"
+	"net/url"
+)
+
+type VerifierImpl struct {
+	expectations    []Expectation
+	firstUnexpected *Request
+}
+
+type Request struct {
+	Name   string // key for the request
+	Method string
+	Url    string
+	Body   interface{}
+}
+
+type ResponseOrError struct {
+	Response aurestclientapi.ParsedResponse
+	Error    error
+}
+
+type Expectation struct {
+	Request  Request
+	Response ResponseOrError
+	Matched  bool
+}
+
+func (e Expectation) matches(method string, requestUrl string, requestBody interface{}) bool {
+	// this is a very simple "must match 100%" for the first version
+	urlMatches := e.Request.Url == requestUrl
+	methodMatches := e.Request.Method == method
+	bodyMatches := requestBodyAsString(e.Request.Body) == requestBodyAsString(requestBody)
+
+	return urlMatches && methodMatches && bodyMatches
+}
+
+func requestBodyAsString(requestBody interface{}) string {
+	if requestBody == nil {
+		return ""
+	}
+	if asCustom, ok := requestBody.(aurestclientapi.CustomRequestBody); ok {
+		if b, err := io.ReadAll(asCustom.BodyReader); err == nil {
+			return string(b)
+		} else {
+			return fmt.Sprintf("ERROR: %s", err.Error())
+		}
+	}
+	if asString, ok := requestBody.(string); ok {
+		return asString
+	}
+	if asUrlValues, ok := requestBody.(url.Values); ok {
+		asString := asUrlValues.Encode()
+		return asString
+	}
+
+	marshalled, err := json.Marshal(requestBody)
+	if err != nil {
+		return fmt.Sprintf("ERROR: %s", err.Error())
+	}
+	return string(marshalled)
+}
+
+func New() (aurestclientapi.Client, *VerifierImpl) {
+	instance := &VerifierImpl{
+		expectations: make([]Expectation, 0),
+	}
+	return instance, instance
+}
+
+func (c *VerifierImpl) Perform(ctx context.Context, method string, requestUrl string, requestBody interface{}, response *aurestclientapi.ParsedResponse) error {
+	expected, err := c.currentExpectation(method, requestUrl, requestBody)
+	if err != nil {
+		return err
+	}
+
+	if expected.Response.Error != nil {
+		return expected.Response.Error
+	}
+
+	mockResponse := expected.Response.Response
+
+	response.Header = mockResponse.Header
+	response.Status = mockResponse.Status
+	response.Time = mockResponse.Time
+	if response.Body != nil && mockResponse.Body != nil {
+		// copy over through json round trip
+		marshalled, _ := json.Marshal(mockResponse.Body)
+		_ = json.Unmarshal(marshalled, response.Body)
+	}
+
+	return nil
+}
+
+func (c *VerifierImpl) currentExpectation(method string, requestUrl string, requestBody interface{}) (Expectation, error) {
+	for i, e := range c.expectations {
+		if !e.Matched {
+			if e.matches(method, requestUrl, requestBody) {
+				c.expectations[i].Matched = true
+				return e, nil
+			} else {
+				if c.firstUnexpected == nil {
+					c.firstUnexpected = &Request{
+						Name:   fmt.Sprintf("unmatched expectation %d - %s", i+1, e.Request.Name),
+						Method: method,
+						Url:    requestUrl,
+						Body:   requestBody,
+					}
+				}
+				return Expectation{}, fmt.Errorf("unmatched expectation %d - %s", i+1, e.Request.Name)
+			}
+		}
+	}
+
+	if c.firstUnexpected == nil {
+		c.firstUnexpected = &Request{
+			Name:   fmt.Sprintf("no expectations remaining - unexpected request at end"),
+			Method: method,
+			Url:    requestUrl,
+			Body:   requestBody,
+		}
+	}
+	return Expectation{}, errors.New("no expectations remaining - unexpected request at end")
+}
+
+func (c *VerifierImpl) AddExpectation(requestMatcher Request, response aurestclientapi.ParsedResponse, err error) {
+	c.expectations = append(c.expectations, Expectation{
+		Request: requestMatcher,
+		Response: ResponseOrError{
+			Response: response,
+			Error:    err,
+		},
+	})
+}
+
+func (c *VerifierImpl) FirstUnexpectedOrNil() *Request {
+	return c.firstUnexpected
+}