diff --git a/spec/models/channel/filter/match/email_regex_spec.rb b/spec/models/channel/filter/match/email_regex_spec.rb
new file mode 100644
index 000000000..88319319c
--- /dev/null
+++ b/spec/models/channel/filter/match/email_regex_spec.rb
@@ -0,0 +1,122 @@
+require 'rails_helper'
+
+RSpec.describe Channel::Filter::Match::EmailRegex do
+  describe '.match' do
+    subject(:match) { Channel::Filter::Match::EmailRegex.match(value: from, match_rule: sender, check_mode: check_mode) }
+    let(:from) { 'foobar@foo.bar' }
+
+    context 'in normal (error-suppressing) mode (default)' do
+      let(:check_mode) { false }
+
+      context 'with exact match' do
+        let(:sender) { 'foobar@foo.bar' }
+
+        it { is_expected.to be(true) }
+      end
+
+      context 'with wildcard *' do
+        let(:sender) { '*' }
+
+        it { is_expected.to be(true) }
+      end
+
+      context 'with empty string' do
+        let(:sender) { '' }
+
+        it { is_expected.to be(true) }
+      end
+
+      context 'with `regex` operator' do
+        context 'and matching regex' do
+          let(:sender) { 'regex:foobar@.*' }
+
+          it { is_expected.to be(true) }
+        end
+
+        context 'and non-matching regex' do
+          let(:sender) { 'regex:nagios@.*' }
+
+          it { is_expected.to be(false) }
+        end
+
+        context 'and invalid regex (misused ? repeat operator)' do
+          let(:sender) { 'regex:??' }
+
+          it { is_expected.to be(false) }
+        end
+
+        context 'and invalid regex (misused ? repeat operator)' do
+          let(:sender) { 'regex:*' }
+
+          it { is_expected.to be(false) }
+        end
+
+        context 'and invalid regex (empty char class)' do
+          let(:sender) { 'regex:[]' }
+
+          it { is_expected.to be(false) }
+        end
+      end
+    end
+
+    context 'in check (error-raising) mode' do
+      let(:check_mode) { true }
+
+      context 'with exact match' do
+        let(:sender) { 'foobar@foo.bar' }
+
+        it { is_expected.to be(true) }
+      end
+
+      context 'with wildcard *' do
+        let(:sender) { '*' }
+
+        it { is_expected.to be(true) }
+      end
+
+      context 'with empty string' do
+        let(:sender) { '' }
+
+        it { is_expected.to be(true) }
+      end
+
+      context 'with `regex` operator' do
+        context 'and matching regex' do
+          let(:sender) { 'regex:foobar@.*' }
+
+          it { is_expected.to be(true) }
+        end
+
+        context 'and non-matching regex' do
+          let(:sender) { 'regex:nagios@.*' }
+
+          it { is_expected.to be(false) }
+        end
+
+        context 'and invalid regex (misused ? repeat operator)' do
+          let(:sender) { 'regex:??' }
+
+          it { expect { subject }.to raise_error(<<~ERR.chomp) }
+            Can't use regex '??' on 'foobar@foo.bar': target of repeat operator is not specified: /??/i
+          ERR
+        end
+
+        context 'and invalid regex (misused ? repeat operator)' do
+          let(:sender) { 'regex:*' }
+
+          it { expect { subject }.to raise_error(<<~ERR.chomp) }
+            Can't use regex '*' on 'foobar@foo.bar': target of repeat operator is not specified: /*/i
+          ERR
+        end
+
+        context 'and invalid regex (empty char class)' do
+          let(:sender) { 'regex:[]' }
+
+          it { expect { subject }.to raise_error(<<~ERR.chomp) }
+            Can't use regex '[]' on 'foobar@foo.bar': empty char-class: /[]/i
+          ERR
+        end
+      end
+    end
+  end
+end
diff --git a/test/unit/email_regex_test.rb b/test/unit/email_regex_test.rb
deleted file mode 100644
index 0389d06e8..000000000
--- a/test/unit/email_regex_test.rb
+++ /dev/null
@@ -1,116 +0,0 @@
-require 'test_helper'
-
-class EmailRegexTest < ActiveSupport::TestCase
-
-  test 'should be able to detect valid/invalid the regex filter' do
-    # check with exact email, check_mode = true
-    sender = 'foobar@foo.bar'
-    from = 'foobar@foo.bar'
-    regex = Channel::Filter::Match::EmailRegex.match(value: from, match_rule: sender, check_mode: true)
-    assert_equal(true, regex)
-
-    # check with exact email
-    sender = 'foobar@foo.bar'
-    from = 'foobar@foo.bar'
-    regex = Channel::Filter::Match::EmailRegex.match(value: from, match_rule: sender, check_mode: false)
-    assert_equal(true, regex)
-
-    # check with regex: filter check_mode = true
-    sender = 'regex:foobar@.*'
-    from = 'foobar@foo.bar'
-    regex = Channel::Filter::Match::EmailRegex.match(value: from, match_rule: sender, check_mode: true)
-    assert_equal(true, regex)
-
-    # check with regex: filter
-    sender = 'regex:foobar@.*'
-    from = 'foobar@foo.bar'
-    regex = Channel::Filter::Match::EmailRegex.match(value: from, match_rule: sender, check_mode: false)
-    assert_equal(true, regex)
-
-    # check regex with regex: filter
-    sender = 'regex:??'
-    from = 'foobar@foo.bar'
-    regex = Channel::Filter::Match::EmailRegex.match(value: from, match_rule: sender, check_mode: false)
-    assert_equal(false, regex)
-
-    # check regex with raise error (check_mode = true)
-    assert_raises("Can't use regex '??' on 'foobar@foo.bar'") do
-      sender = 'regex:??'
-      from = 'foobar@foo.bar'
-      regex = Channel::Filter::Match::EmailRegex.match(value: from, match_rule: sender, check_mode: true)
-    end
-
-    sender = 'regex:[]'
-    from = 'foobar@foo.bar'
-    regex = Channel::Filter::Match::EmailRegex.match(value: from, match_rule: sender, check_mode: false)
-    assert_equal(false, regex)
-
-    # check regex with raise error, (check_mode = true)
-    assert_raises("Can't use regex '[]' on 'foobar@foo.bar'") do
-      sender = 'regex:[]'
-      from = 'foobar@foo.bar'
-      regex = Channel::Filter::Match::EmailRegex.match(value: from, match_rule: sender, check_mode: true)
-    end
-
-    # check regex with empty field
-    sender = '{}'
-    from = 'foobar@foo.bar'
-    regex = Channel::Filter::Match::EmailRegex.match(value: from, match_rule: sender, check_mode: false)
-    assert_equal(false, regex)
-
-    # check regex with empty field and raise error (check_mode = true)
-    sender = '{}'
-    from = 'foobar@foo.bar'
-    regex = Channel::Filter::Match::EmailRegex.match(value: from, match_rule: sender, check_mode: true)
-    assert_equal(false, regex)
-
-    # check regex with empty field
-    sender = ''
-    from = 'foobar@foo.bar'
-    regex = Channel::Filter::Match::EmailRegex.match(value: from, match_rule: sender, check_mode: false)
-    assert_equal(true, regex)
-
-    # check regex with empty field
-    sender = ''
-    from = 'foobar@foo.bar'
-    regex = Channel::Filter::Match::EmailRegex.match(value: from, match_rule: sender, check_mode: true)
-    assert_equal(true, regex)
-
-    # check regex with regex: wildcard
-    sender = 'regex:*'
-    from = 'foobar@foo.bar'
-    regex = Channel::Filter::Match::EmailRegex.match(value: from, match_rule: sender, check_mode: false)
-    assert_equal(false, regex)
-
-    # check regex with regex: wildcard and raise error (check_mode = true)
-    assert_raises("Can't use regex '*' on 'foobar@foo.bar'") do
-      sender = 'regex:*'
-      from = 'foobar@foo.bar'
-      regex = Channel::Filter::Match::EmailRegex.match(value: from, match_rule: sender, check_mode: true)
-    end
-
-    # check email with wildcard
-    sender = '*'
-    from = 'foobar@foo.bar'
-    regex = Channel::Filter::Match::EmailRegex.match(value: from, match_rule: sender, check_mode: false)
-    assert_equal(true, regex)
-
-    # check email with wildcard (check_mode = true)
-    sender = '*'
-    from = 'foobar@foo.bar'
-    regex = Channel::Filter::Match::EmailRegex.match(value: from, match_rule: sender, check_mode: true)
-    assert_equal(true, regex)
-
-    # check email with a different sender
-    sender = 'regex:nagios@.*'
-    from = 'foobar@foo.bar'
-    regex = Channel::Filter::Match::EmailRegex.match(value: from, match_rule: sender, check_mode: false)
-    assert_equal(false, regex)
-
-    # check email with a different sender with checkmode = true
-    sender = 'regex:nagios@.*'
-    from = 'foobar@foo.bar'
-    regex = Channel::Filter::Match::EmailRegex.match(value: from, match_rule: sender, check_mode: true)
-    assert_equal(false, regex)
-  end
-end