Wrote tests for the rsa.go file (cadence-workflow#1386)

What changed?
Wrote tests for rsa.go (now 85.7% according to goland)

Some of the error cases in loadRSAKey are not reachable without manipulating the key bytes to trigger them. I didn't do those

Why?
Improve code coverage

How did you test it?

Potential risks

Author: jakobht

internal/common/util/rsa_test.go

@@ -0,0 +1,80 @@
+// Copyright (c) 2017-2021 Uber Technologies Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package util
+
+import (
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func loadTestKeyFile(t *testing.T, path string) []byte {
+	t.Helper()
+	key, err := os.ReadFile(path)
+	require.NoError(t, err)
+	return key
+}
+
+func TestLoadRSAPublicKey(t *testing.T) {
+	publicKeyPEM := loadTestKeyFile(t, "./../auth/credentials/keytest.pub")
+
+	t.Run("valid public key", func(t *testing.T) {
+		key, err := LoadRSAPublicKey(publicKeyPEM)
+		assert.NoError(t, err)
+		assert.NotNil(t, key)
+		assert.Equal(t, 2048, key.Size()*8)
+	})
+
+	t.Run("invalid public key", func(t *testing.T) {
+		_, err := LoadRSAPublicKey([]byte("invalid PEM data"))
+		assert.ErrorContains(t, err, "failed to parse PEM block containing the public key")
+	})
+
+	t.Run("incorrect PEM type for public key", func(t *testing.T) {
+		privateKeyPEM := loadTestKeyFile(t, "./../auth/credentials/keytest")
+		_, err := LoadRSAPublicKey(privateKeyPEM)
+		assert.ErrorContains(t, err, "failed to parse PEM block containing the public key")
+	})
+}
+
+func TestLoadRSAPrivateKey(t *testing.T) {
+	privateKeyPEM := loadTestKeyFile(t, "./../auth/credentials/keytest")
+
+	t.Run("valid private key", func(t *testing.T) {
+		key, err := LoadRSAPrivateKey(privateKeyPEM)
+		assert.NoError(t, err)
+		assert.NotNil(t, key)
+		assert.Equal(t, 2048, key.Size()*8)
+	})
+
+	t.Run("invalid private key", func(t *testing.T) {
+		_, err := LoadRSAPrivateKey([]byte("invalid PEM data"))
+		assert.ErrorContains(t, err, "failed to parse PEM block containing the private key")
+	})
+
+	t.Run("incorrect PEM type for private key", func(t *testing.T) {
+		publicKeyPEM := loadTestKeyFile(t, "./../auth/credentials/keytest.pub")
+		_, err := LoadRSAPrivateKey(publicKeyPEM)
+		assert.ErrorContains(t, err, "failed to parse PEM block containing the private key")
+	})
+}