feat: add Regex() matcher (#114)

Add a matcher for matching against regular expressions

gomock/matchers.go

@@ -17,6 +17,7 @@ package gomock
 import (
 	"fmt"
 	"reflect"
+	"regexp"
 	"strings"
 )
 
@@ -168,6 +169,25 @@ func (n notMatcher) String() string {
 	return "not(" + n.m.String() + ")"
 }
 
+type regexMatcher struct {
+	regex *regexp.Regexp
+}
+
+func (m regexMatcher) Matches(x any) bool {
+	switch t := x.(type) {
+	case string:
+		return m.regex.MatchString(t)
+	case []byte:
+		return m.regex.Match(t)
+	default:
+		return false
+	}
+}
+
+func (m regexMatcher) String() string {
+	return "matches regex " + m.regex.String()
+}
+
 type assignableToTypeOfMatcher struct {
 	targetType reflect.Type
 }
@@ -382,6 +402,18 @@ func Not(x any) Matcher {
 	return notMatcher{Eq(x)}
 }
 
+// Regex checks whether parameter matches the associated regex.
+//
+// Example usage:
+//
+//	Regex("[0-9]{2}:[0-9]{2}").Matches("23:02") // returns true
+//	Regex("[0-9]{2}:[0-9]{2}").Matches([]byte{'2', '3', ':', '0', '2'}) // returns true
+//	Regex("[0-9]{2}:[0-9]{2}").Matches("hello world") // returns false
+//	Regex("[0-9]{2}").Matches(21) // returns false as it's not a valid type
+func Regex(regexStr string) Matcher {
+	return regexMatcher{regex: regexp.MustCompile(regexStr)}
+}
+
 // AssignableToTypeOf is a Matcher that matches if the parameter to the mock
 // function is assignable to the type of the parameter to this function.
 //

gomock/matchers_test.go

@@ -47,6 +47,7 @@ func TestMatchers(t *testing.T) {
 			[]e{nil, (error)(nil), (chan bool)(nil), (*int)(nil)},
 			[]e{"", 0, make(chan bool), errors.New("err"), new(int)}},
 		{"test Not", gomock.Not(gomock.Eq(4)), []e{3, "blah", nil, int64(4)}, []e{4}},
+		{"test Regex", gomock.Regex("[0-9]{2}:[0-9]{2}"), []e{"23:02", "[23:02]: Hello world", []byte("23:02")}, []e{4, "23-02", "hello world", true, []byte("23-02")}},
 		{"test All", gomock.All(gomock.Any(), gomock.Eq(4)), []e{4}, []e{3, "blah", nil, int64(4)}},
 		{"test Len", gomock.Len(2),
 			[]e{[]int{1, 2}, "ab", map[string]int{"a": 0, "b": 1}, [2]string{"a", "b"}},
@@ -92,6 +93,65 @@ func TestNotMatcher(t *testing.T) {
 	}
 }
 
+// A more thorough test of regexMatcher
+func TestRegexMatcher(t *testing.T) {
+	tests := []struct {
+		name               string
+		regex              string
+		input              any
+		wantMatch          bool
+		wantStringResponse string
+		shouldPanic        bool
+	}{
+		{
+			name:               "match for whole num regex with start and end position matching",
+			regex:              "^\\d+$",
+			input:              "2302",
+			wantMatch:          true,
+			wantStringResponse: "matches regex ^\\d+$",
+		},
+		{
+			name:               "match for valid regex with start and end position matching on longer string",
+			regex:              "^[0-9]{2}:[0-9]{2}$",
+			input:              "[23:02]: Hello world",
+			wantMatch:          false,
+			wantStringResponse: "matches regex ^[0-9]{2}:[0-9]{2}$",
+		},
+		{
+			name:               "match for valid regex with struct as bytes",
+			regex:              `^{"id":[0-9]{2}}$`,
+			input:              []byte{'{', '"', 'i', 'd', '"', ':', '1', '2', '}'},
+			wantMatch:          true,
+			wantStringResponse: `matches regex ^{"id":[0-9]{2}}$`,
+		},
+		{
+			name:        "should panic when regex fails to compile",
+			regex:       `^[0-9]\\?{2}:[0-9]{2}$`,
+			shouldPanic: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if tt.shouldPanic {
+				defer func() { _ = recover() }()
+			}
+			matcher := gomock.Regex(tt.regex)
+
+			if tt.shouldPanic {
+				t.Errorf("test did not panic, and should have")
+			}
+
+			if got := matcher.Matches(tt.input); got != tt.wantMatch {
+				t.Errorf("got = %v, wantMatch = %v", got, tt.wantMatch)
+			}
+			if gotStr := matcher.String(); gotStr != tt.wantStringResponse {
+				t.Errorf("got string = %v, want string = %v", gotStr, tt.wantStringResponse)
+			}
+		})
+	}
+}
+
 type Dog struct {
 	Breed, Name string
 }