diff --git a/tests/Mutator/Extensions/MBStringTest.php b/tests/Mutator/Extensions/MBStringTest.php
index f65fac191..298c7bdb5 100644
--- a/tests/Mutator/Extensions/MBStringTest.php
+++ b/tests/Mutator/Extensions/MBStringTest.php
@@ -126,6 +126,11 @@ private function provideMutationCasesForChr(): Generator
             "<?php\n\nchr(74);",
         ];
 
+        yield 'It converts correctly when mb_chr is wrongly capitalized' => [
+            '<?php mB_cHr(74);',
+            "<?php\n\nchr(74);",
+        ];
+
         yield 'It converts mb_chr with encoding to chr' => [
             "<?php mb_chr(74, 'utf-8');",
             "<?php\n\nchr(74);",
@@ -139,6 +144,11 @@ private function provideMutationCasesForOrd(): Generator
             "<?php\n\nord('T');",
         ];
 
+        yield 'It converts correctly when mb_ord is wrongly capitalized' => [
+            "<?php MB_ord('T');",
+            "<?php\n\nord('T');",
+        ];
+
         yield 'It converts mb_ord with encoding to ord' => [
             "<?php mb_ord('T', 'utf-8');",
             "<?php\n\nord('T');",
@@ -152,6 +162,11 @@ private function provideMutationCasesForParseStr(): Generator
             "<?php\n\nparse_str('T');",
         ];
 
+        yield 'It converts correctly when mb_parse_str is wrongly capitalize' => [
+            "<?php mb_pARse_Str('T');",
+            "<?php\n\nparse_str('T');",
+        ];
+
         yield 'It converts mb_parse_str with params argument to parse_str' => [
             "<?php mb_parse_str('T', \$params);",
             "<?php\n\nparse_str('T', \$params);",
@@ -165,6 +180,11 @@ private function provideMutationCasesForSendMail(): Generator
             "<?php\n\nmail('to', 'subject', 'msg');",
         ];
 
+        yield 'It converts correctly when mb_send_mail is wrongly capitalize' => [
+            "<?php mb_SEND_mail('to', 'subject', 'msg');",
+            "<?php\n\nmail('to', 'subject', 'msg');",
+        ];
+
         yield 'It converts mb_send_mail with additional parameters to mail' => [
             "<?php mb_send_mail('to', 'subject', 'msg', [], []);",
             "<?php\n\nmail('to', 'subject', 'msg', [], []);",
@@ -178,6 +198,11 @@ private function provideMutationCasesForStrCut(): Generator
             "<?php\n\nsubstr('subject', 1);",
         ];
 
+        yield 'It converts correctly when mb_strcut is wrongly capitalize' => [
+            "<?php MB_strcut('subject', 1);",
+            "<?php\n\nsubstr('subject', 1);",
+        ];
+
         yield 'It converts mb_strcut with limit to substr' => [
             "<?php mb_strcut('subject', 1, 20);",
             "<?php\n\nsubstr('subject', 1, 20);",
@@ -196,6 +221,11 @@ private function provideMutationCasesForStrPos(): Generator
             "<?php\n\nstrpos('subject', 'b');",
         ];
 
+        yield 'It converts correctly when mb_strpos is wrongly capitalize' => [
+            "<?php mb_StRpOs('subject', 'b');",
+            "<?php\n\nstrpos('subject', 'b');",
+        ];
+
         yield 'It converts mb_strpos with offset to strpos' => [
             "<?php mb_strpos('subject', 'b', 3);",
             "<?php\n\nstrpos('subject', 'b', 3);",
@@ -214,6 +244,11 @@ private function provideMutationCasesForStrIPos(): Generator
             "<?php\n\nstripos('subject', 'b');",
         ];
 
+        yield 'It converts correctly when mb_stripos is wrongly capitalize' => [
+            "<?php mB_sTRIpos('subject', 'b');",
+            "<?php\n\nstripos('subject', 'b');",
+        ];
+
         yield 'It converts mb_stripos with offset to stripos' => [
             "<?php mb_stripos('subject', 'b', 3);",
             "<?php\n\nstripos('subject', 'b', 3);",
@@ -232,6 +267,11 @@ private function provideMutationCasesForStrIStr(): Generator
             "<?php\n\nstristr('subject', 'b');",
         ];
 
+        yield 'It converts correctly when mb_stristr is wrongly capitalize' => [
+            "<?php mb_strISTR('subject', 'b');",
+            "<?php\n\nstristr('subject', 'b');",
+        ];
+
         yield 'It converts mb_stristr with part argument to stristr' => [
             "<?php mb_stristr('subject', 'b', false);",
             "<?php\n\nstristr('subject', 'b', false);",
@@ -250,6 +290,11 @@ private function provideMutationCasesForStrRiPos(): Generator
             "<?php\n\nstrripos('subject', 'b');",
         ];
 
+        yield 'It converts correctly when mb_strripos is wrongly capitalize' => [
+            "<?php MB_sTrRipos('subject', 'b');",
+            "<?php\n\nstrripos('subject', 'b');",
+        ];
+
         yield 'It converts mb_strripos with offset argument to strripos' => [
             "<?php mb_strripos('subject', 'b', 2);",
             "<?php\n\nstrripos('subject', 'b', 2);",
@@ -268,6 +313,11 @@ private function provideMutationCasesForStrRPos(): Generator
             "<?php\n\nstrrpos('subject', 'b');",
         ];
 
+        yield 'It converts correctly when mb_strrpos is wrongly capitalize' => [
+            "<?php mb_StRrPos('subject', 'b');",
+            "<?php\n\nstrrpos('subject', 'b');",
+        ];
+
         yield 'It converts mb_strrpos with offset argument to strrpos' => [
             "<?php mb_strrpos('subject', 'b', 2);",
             "<?php\n\nstrrpos('subject', 'b', 2);",
@@ -286,6 +336,11 @@ private function provideMutationCasesForStrStr(): Generator
             "<?php\n\nstrstr('subject', 'b');",
         ];
 
+        yield 'It converts correctly when mb_strstr is wrongly capitalize' => [
+            "<?php Mb_STRstr('subject', 'b');",
+            "<?php\n\nstrstr('subject', 'b');",
+        ];
+
         yield 'It converts mb_strstr with part argument to strstr' => [
             "<?php mb_strstr('subject', 'b', false);",
             "<?php\n\nstrstr('subject', 'b', false);",
@@ -304,6 +359,11 @@ private function provideMutationCasesForStrToLower(): Generator
             "<?php\n\nstrtolower('test');",
         ];
 
+        yield 'It converts correctly when mb_strtolower is wrongly capitalize' => [
+            "<?php mB_StrTOloWer('test');",
+            "<?php\n\nstrtolower('test');",
+        ];
+
         yield 'It converts mb_strtolower with encoding to strtolower' => [
             "<?php mb_strtolower('test', 'utf-8');",
             "<?php\n\nstrtolower('test');",
@@ -317,6 +377,11 @@ private function provideMutationCasesForStrToUpper(): Generator
             "<?php\n\nstrtoupper('test');",
         ];
 
+        yield 'It converts correctly when mb_strtoupper is wrongly capitalize' => [
+            "<?php Mb_StrToupPer('test');",
+            "<?php\n\nstrtoupper('test');",
+        ];
+
         yield 'It converts mb_strtoupper with encoding to strtoupper' => [
             "<?php mb_strtoupper('test', 'utf-8');",
             "<?php\n\nstrtoupper('test');",
@@ -330,6 +395,11 @@ private function provideMutationCasesForSubStrCount(): Generator
             "<?php\n\nsubstr_count('test', 't');",
         ];
 
+        yield 'It converts correctly when mb_substr_count is wrongly capitalize' => [
+            "<?php MB_substr_COunt('test', 't');",
+            "<?php\n\nsubstr_count('test', 't');",
+        ];
+
         yield 'It converts mb_substr_count with encoding to substr_count' => [
             "<?php mb_substr_count('test', 't', 'utf-8');",
             "<?php\n\nsubstr_count('test', 't');",
@@ -343,6 +413,11 @@ private function provideMutationCasesForSubStr(): Generator
             "<?php\n\nsubstr('test', 2);",
         ];
 
+        yield 'It converts correctly when mb_substr is wrongly capitalize' => [
+            "<?php mB_SuBsTr('test', 2);",
+            "<?php\n\nsubstr('test', 2);",
+        ];
+
         yield 'It converts mb_substr with length argument to substr' => [
             "<?php mb_substr('test', 2, 10);",
             "<?php\n\nsubstr('test', 2, 10);",
@@ -361,6 +436,11 @@ private function provideMutationCasesForStrRChr(): Generator
             "<?php\n\nstrrchr('subject', 'b');",
         ];
 
+        yield 'It converts correctly when mb_strrchr is wrongly capitalize' => [
+            "<?php MB_StRrcHr('subject', 'b');",
+            "<?php\n\nstrrchr('subject', 'b');",
+        ];
+
         yield 'It converts mb_strrchr with part argument to strrchr' => [
             "<?php mb_strrchr('subject', 'b', false);",
             "<?php\n\nstrrchr('subject', 'b');",
@@ -379,6 +459,11 @@ private function provideMutationCasesForConvertCase(): Generator
             "<?php\n\nstrtoupper('test');",
         ];
 
+        yield 'It converts correctly when mb_parse_str is wrongly capitalize' => [
+            "<?php Mb_CoNvErT_Case('test', MB_CASE_UPPER);",
+            "<?php\n\nstrtoupper('test');",
+        ];
+
         yield 'It converts mb_convert_case with MB_CASE_UPPER_SIMPLE mode to strtoupper' => [
             "<?php mb_convert_case('test', MB_CASE_UPPER_SIMPLE);",
             "<?php\n\nstrtoupper('test');",