diff --git a/k9mail-library/src/test/java/com/fsck/k9/mail/internet/DecoderUtilTest.java b/k9mail-library/src/test/java/com/fsck/k9/mail/internet/DecoderUtilTest.java
index cd693c3be..0cd4fc893 100644
--- a/k9mail-library/src/test/java/com/fsck/k9/mail/internet/DecoderUtilTest.java
+++ b/k9mail-library/src/test/java/com/fsck/k9/mail/internet/DecoderUtilTest.java
@@ -12,112 +12,173 @@ import static org.junit.Assert.assertEquals;
 @RunWith(K9LibRobolectricTestRunner.class)
 public class DecoderUtilTest {
 
-    @Test
-    public void testDecodeEncodedWords() {
-        String body, expect;
-        MimeMessage message;
+    private String body, expect;
+    private MimeMessage message;
 
+    @Test
+    public void decodeEncodedWords_with_unencoded_data_returns_original_text() {
         body = "abc";
         expect = "abc";
         message = null;
         assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+    }
+
+    @Test
+    public void decodeEncodedWords_withAsciiCharset_encoded_data_returns_text() {
 
         body = "=?us-ascii?q?abc?=";
         expect = "abc";
         message = null;
         assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+    }
 
+    @Test
+    public void decodeEncodedWords_withStartOnly_encoding_format_returnAsText() {
         body = "=?";
         expect = "=?";
         message = null;
         assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+    }
 
+    @Test
+    public void decodeEncodedWords_withStartAndSeparatorOnly_returnAsText() {
         body = "=??";
         expect = "=??";
         message = null;
         assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+    }
 
+    @Test
+    public void decodeEncodedWords_withStartAnd2SeparatorOnly_returnAsText() {
         body = "=???";
         expect = "=???";
         message = null;
         assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+    }
 
+    @Test
+    public void decodeEncodedWords_withStartAnd3SeparatorOnly_returnAsText() {
         body = "=????";
         expect = "=????";
         message = null;
         assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+    }
 
+    @Test
+    public void decodeEncodedWords_withSeparatorsOnly_returnAsText() {
         body = "=????=";
         expect = "=????=";
         message = null;
         assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+    }
 
+    @Test
+    public void decodeEncodedWords_withMissingCharset_returnAsText() {
         body = "=??q??=";
         expect = "=??q??=";
         ;
         message = null;
         assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+    }
+
+    @Test
+    public void decodeEncodedWords_withTextAndMissingCharset_returnAsText() {
 
         body = "=??q?a?=";
         expect = "a";
         message = null;
         assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+    }
+
+    @Test
+    public void decodeEncodedWords_withNoTextCharsetOrEncoding_returnAsText() {
 
         body = "=??=";
         expect = "=??=";
         message = null;
         assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+    }
+
+    @Test
+    public void decodeEncodedWords_with_MissingEncodingAndData_returnAsText() {
 
         body = "=?x?=";
         expect = "=?x?=";
         message = null;
         assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+    }
+
+    @Test
+    public void decodeEncodedWords_withMissingEncoding_returnAsText() {
 
         body = "=?x??=";
         expect = "=?x??=";
         message = null;
         assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+    }
+
+    @Test
+    public void decodeEncodedWords_with_incompleteEncodingFormat_returnAsText() {
 
         body = "=?x?q?=";
         expect = "=?x?q?=";
         message = null;
         assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+    }
+
+    @Test
+    public void decodeEncodedWords_with_unrecognisedEncoding_withEmptyEncodedData_returnAsText() {
 
         body = "=?x?q??=";
         expect = "=?x?q??=";
         message = null;
         assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+    }
+
+    @Test
+    public void decodeEncodedWords_withUnrecognisedEncoding_withEncodedData_return_encoded_data() {
 
         body = "=?x?q?X?=";
         expect = "X";
         message = null;
         assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+    }
 
-        // invalid base64 string
+    @Test
+    public void decodeEncodedWords_withInvalidBase64String_returnsEmptyString() {
         body = "=?us-ascii?b?abc?=";
         expect = "";
         message = null;
         assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+    }
 
-        // broken encoded header
+    @Test
+    public void decodeEncodedWords_withBrokenEncoding_returnsEncodedData() {
         body = "=?us-ascii?q?abc?= =?";
         expect = "abc =?";
         message = null;
         assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+    }
 
+    @Test
+    public void decodeEncodedWords_withUnrecognisedCharset_returnsEncodedData() {
         body = "=?x?= =?";
         expect = "=?x?= =?";
         message = null;
         assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+    }
 
-        //Multi encoded header
+    @Test
+    public void decodeEncodedWords_withMultipleEncodedSections_decodesAll() {
         body = "=?utf-8?B?5Liq5Lq66YKu566xOkJVRyAjMzAyNDY6OumCruS7tuato+aWh+mZhOS7tuWQ?=\n" +
                 "=?utf-8?B?jeensOecgeeVpeaYvuekuuS8mOWMlg==?=";
         expect = "个人邮箱:BUG #30246::邮件正文附件��称省略显示优化";
         message = null;
         assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+    }
 
-        //Non utf-8 encoding
+    @Test
+    public void decodeEncodedWords_withGB2312_decodes_correctly() {
         body = "=?gb2312?B?Obv9t9az6cnu29rHsLqju6rHyLPHSlfN8rrAvsa16qOsuPzT0DIwvNIzOTnU?= " +
                 "=?gb2312?B?qr6r0aG439DHytTLr77Gteq1yMTjwLSjoaOoQUSjqQ?=";
         expect = "9积分抽深圳前海华侨城JW万豪酒店，更有20家399��精选高星试睡酒店等你来！（AD�";