Expect regex find show output on regex match fail

gexpect.go

@@ -213,7 +213,7 @@ func (expect *ExpectSubprocess) expectRegexFind(regex string, output bool) ([]st
 	// convert indexes to strings
 
 	if len(result) == 0 {
-		err = fmt.Errorf("ExpectRegex didn't find regex '%v'.", regex)
+		err = fmt.Errorf("ExpectRegex didn't find regex '%v'.\nOutput:\n%s", regex, stringIndexedInto)
 	} else {
 		// The number in pairs[1] is an index of a first
 		// character outside the whole match
@@ -387,7 +387,7 @@ func (expect *ExpectSubprocess) ReadUntil(delim byte) ([]byte, error) {
 		for i := 0; i < n; i++ {
 			if chunk[i] == delim {
 				if len(chunk) > i+1 {
-					expect.buf.PutBack(chunk[i+1:n])
+					expect.buf.PutBack(chunk[i+1 : n])
 				}
 				return join, nil
 			} else {

gexpect_test.go

@@ -188,6 +188,38 @@ func TestRegexFind(t *testing.T) {
 	}
 }
 
+// TestRegexFindFailure checks to ensure that when ExpectRegexFind()
+// fails, the returned error contains both the regex and the collected
+// output.
+func TestRegexFindFailure(t *testing.T) {
+	input := "hello world"
+	re := "this does not match"
+
+	child, err := Spawn("echo \"" + input + "\"")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	matches, err := child.ExpectRegexFind(re)
+	if err == nil {
+		t.Errorf("Expected error object")
+	}
+
+	if len(matches) > 0 {
+		t.Errorf("Expected no matches, got %v", matches)
+	}
+
+	s := err.Error()
+
+	if strings.Contains(s, re) == false {
+		t.Errorf("Expected error object to contain regex %q, got %v", re, s)
+	}
+
+	if strings.Contains(s, input) == false {
+		t.Errorf("Expected error object to contain input data %q, got %v", input, s)
+	}
+}
+
 func TestReadLine(t *testing.T) {
 	t.Logf("Testing ReadLine...")