Add support for body contains assertion

_testdata/Dynamic.feature

@@ -19,6 +19,10 @@ Feature: Dynamic data is used in steps
      "created_at":"<ignore-diff>","updated_at": "<ignore-diff>"
     }
     """
+    And I should have response with body, that contains 
+    """
+    "id":"$user_id"
+    """
 
     # Creating an order for that user with $user_id.
     When I request HTTP endpoint with method "POST" and URI "/order/$user_id/?user_id=$user_id"
@@ -43,4 +47,4 @@ Feature: Dynamic data is used in steps
      "user_id":"$user_id",
      "prefixed_user": "static_prefix::$user"
     }
-    """
+    """

_testdata/LocalClient.feature

@@ -63,6 +63,10 @@ Feature: HTTP Service
     And I should have other responses with body, that matches JSON paths
       | $.status | "failed" |
       | $.error  | "foo"    |
+    And I should have other responses with body, that contains
+    """
+    "status":"failed"
+    """
 
     And I should have other responses with header "Content-Type: application/json"
 
@@ -128,4 +132,9 @@ Feature: HTTP Service
     """
     And I should have "some-service" response with header "Content-Type: application/json"
 
+    And I should have "some-service" response with body, that contains
+    """
+    some
+    """
+
 

local_client.go

@@ -212,6 +212,7 @@
 
 	s.Step(`^I should have(.*) response with body from file$`, l.iShouldHaveResponseWithBodyFromFile)
 	s.Step(`^I should have(.*) response with body$`, l.iShouldHaveResponseWithBody)
+	s.Step(`^I should have(.*) response with body, that contains$`, l.iShouldHaveResponseWithBodyThatContains)
 	s.Step(`^I should have(.*) response with body, that matches JSON from file$`, l.iShouldHaveResponseWithBodyThatMatchesJSONFromFile)
 	s.Step(`^I should have(.*) response with body, that matches JSON$`, l.iShouldHaveResponseWithBodyThatMatchesJSON)
 	s.Step(`^I should have(.*) response with body, that matches JSON paths$`, l.iShouldHaveResponseWithBodyThatMatchesJSONPaths)
@@ -220,6 +221,7 @@
 	s.Step(`^I should have(.*) other responses with header "([^"]*): ([^"]*)"$`, l.iShouldHaveOtherResponsesWithHeader)
 	s.Step(`^I should have(.*) other responses with headers$`, l.iShouldHaveOtherResponsesWithHeaders)
 	s.Step(`^I should have(.*) other responses with body$`, l.iShouldHaveOtherResponsesWithBody)
+	s.Step(`^I should have(.*) other responses with body, that contains$`, l.iShouldHaveOtherResponsesWithBodyThatContains)
 	s.Step(`^I should have(.*) other responses with body from file$`, l.iShouldHaveOtherResponsesWithBodyFromFile)
 	s.Step(`^I should have(.*) other responses with body, that matches JSON$`, l.iShouldHaveOtherResponsesWithBodyThatMatchesJSON)
 	s.Step(`^I should have(.*) other responses with body, that matches JSON from file$`, l.iShouldHaveOtherResponsesWithBodyThatMatchesJSONFromFile)
@@ -553,6 +555,7 @@
 	errUnexpectedExpectations = sentinelError("unexpected existing expectations")
 	errInvalidNumberOfColumns = sentinelError("invalid number of columns")
 	errUnexpectedBody         = sentinelError("unexpected body")
+	errDoesNotContain         = sentinelError("does not contain")
 )
 
 func statusCode(statusOrCode string) (int, error) {
@@ -740,6 +743,40 @@
 	})
 }
 
+func (l *LocalClient) contains(ctx context.Context, received []byte, bodyDoc string) error {
+	ctx, rv, err := l.VS.Replace(ctx, []byte(bodyDoc))
+	if err != nil {
+		return err
+	}
+
+	s, substr := string(received), string(rv)
+	if !strings.Contains(s, substr) {
+		return augmentBodyErr(ctx, fmt.Errorf("%w %q in %q", errDoesNotContain, substr, s))
+	}
+
+	return nil
+}
+
+func (l *LocalClient) iShouldHaveResponseWithBodyThatContains(ctx context.Context, service, bodyDoc string) (context.Context, error) {
+	ctx = l.VS.PrepareContext(ctx)
+
+	return l.expectResponse(ctx, service, func(c *httpmock.Client) error {
+		return c.ExpectResponseBodyCallback(func(received []byte) error {
+			return l.contains(ctx, received, bodyDoc)
+		})
+	})
+}
+
+func (l *LocalClient) iShouldHaveOtherResponsesWithBodyThatContains(ctx context.Context, service, bodyDoc string) (context.Context, error) {
+	ctx = l.VS.PrepareContext(ctx)
+
+	return l.expectResponse(ctx, service, func(c *httpmock.Client) error {
+		return c.ExpectOtherResponsesBodyCallback(func(received []byte) error {
+			return l.contains(ctx, received, bodyDoc)
+		})
+	})
+}
+
 func (l *LocalClient) iShouldHaveResponseWithBodyFromFile(ctx context.Context, service, filePath string) (context.Context, error) {
 	ctx = l.VS.PrepareContext(ctx)