diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index 6c87ad82955..b07c21fa4cb 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -115,6 +115,15 @@ namespace ts {
         return -1;
     }
 
+    export function firstOrUndefined<T>(array: T[], predicate: (x: T) => boolean): T {
+        for (let i = 0, len = array.length; i < len; i++) {
+            if (predicate(array[i])) {
+                return array[i];
+            }
+        }
+        return undefined;
+    }
+
     export function indexOfAnyCharCode(text: string, charCodes: number[], start?: number): number {
         for (let i = start || 0, len = text.length; i < len; i++) {
             if (contains(charCodes, text.charCodeAt(i))) {
diff --git a/src/compiler/diagnosticMessages.json b/src/compiler/diagnosticMessages.json
index 8126d5c605e..1dffc35c74c 100644
--- a/src/compiler/diagnosticMessages.json
+++ b/src/compiler/diagnosticMessages.json
@@ -3031,5 +3031,33 @@
     "Unknown typing option '{0}'.": {
         "category": "Error",
         "code": 17010
+    },
+    "Add missing 'super()' call.": {
+        "category": "CodeFix",
+        "code": 90001
+    },
+    "Make 'super()' call the first statement in the constructor.": {
+        "category": "CodeFix",
+        "code": 90002
+    },
+    "Change 'extends' to 'implements'": {
+        "category": "CodeFix",
+        "code": 90003
+    },
+    "Remove unused identifiers": {
+        "category": "CodeFix",
+        "code": 90004
+    },
+    "Implement interface on reference": {
+        "category": "CodeFix",
+        "code": 90005
+    },
+    "Implement interface on class": {
+        "category": "CodeFix",
+        "code": 90006
+    },
+    "Implement inherited abstract class": {
+        "category": "CodeFix",
+        "code": 90007
     }
 }
diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index 28ededebb0d..e31a4b0ace1 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -2547,6 +2547,7 @@ namespace ts {
         Warning,
         Error,
         Message,
+        CodeFix,
     }
 
     export enum ModuleResolutionKind {
diff --git a/src/harness/fourslash.ts b/src/harness/fourslash.ts
index a42abbbc609..91597d7f593 100644
--- a/src/harness/fourslash.ts
+++ b/src/harness/fourslash.ts
@@ -384,7 +384,7 @@ namespace FourSlash {
 
             if (exists !== negative) {
                 this.printErrorLog(negative, this.getAllDiagnostics());
-                throw new Error("Failure between markers: " + startMarkerName + ", " + endMarkerName);
+                throw new Error(`Failure between markers: '${startMarkerName}', '${endMarkerName}'`);
             }
         }
 
@@ -638,7 +638,6 @@ namespace FourSlash {
             }
         }
 
-
         public verifyCompletionListAllowsNewIdentifier(negative: boolean) {
             const completions = this.getCompletionListAtCaret();
 
@@ -1479,7 +1478,7 @@ namespace FourSlash {
             if (isFormattingEdit) {
                 const newContent = this.getFileContent(fileName);
 
-                if (newContent.replace(/\s/g, "") !== oldContent.replace(/\s/g, "")) {
+                if (this.removeWhitespace(newContent) !== this.removeWhitespace(oldContent)) {
                     this.raiseError("Formatting operation destroyed non-whitespace content");
                 }
             }
@@ -1545,6 +1544,10 @@ namespace FourSlash {
             }
         }
 
+        private removeWhitespace(text: string): string {
+            return text.replace(/\s/g, "");
+        }
+
         public goToBOF() {
             this.goToPosition(0);
         }
@@ -1862,6 +1865,44 @@ namespace FourSlash {
             }
         }
 
+        public verifyCodeFixAtPosition(expectedText: string, errorCode?: number) {
+
+            const ranges = this.getRanges();
+            if (ranges.length == 0) {
+                this.raiseError("At least one range should be specified in the testfile.");
+            }
+
+            const fileName = this.activeFile.fileName;
+            const diagnostics = this.getDiagnostics(fileName);
+
+            if (diagnostics.length === 0) {
+                this.raiseError("Errors expected.");
+            }
+
+            if (diagnostics.length > 1 && !errorCode) {
+                this.raiseError("When there's more than one error, you must specify the errror to fix.");
+            }
+
+            const diagnostic = !errorCode ? diagnostics[0] : ts.firstOrUndefined(diagnostics, d => d.code == errorCode);
+
+            const actual = this.languageService.getCodeFixesAtPosition(fileName, diagnostic.start, diagnostic.length, [`TS${diagnostic.code}`]);
+
+            if (!actual || actual.length == 0) {
+                this.raiseError("No codefixes returned.");
+            }
+
+            if (actual.length > 1) {
+                this.raiseError("More than 1 codefix returned.");
+            }
+
+            this.applyEdits(actual[0].changes[0].fileName, actual[0].changes[0].textChanges, /*isFormattingEdit*/ false);
+            const actualText = this.rangeText(ranges[0]);
+
+            if (this.removeWhitespace(actualText) !== this.removeWhitespace(expectedText)) {
+                this.raiseError(`Actual text doesn't match expected text. Actual: '${actualText}' Expected: '${expectedText}'`);
+            }
+        }
+
         public verifyDocCommentTemplate(expected?: ts.TextInsertion) {
             const name = "verifyDocCommentTemplate";
             const actual = this.languageService.getDocCommentTemplateAtPosition(this.activeFile.fileName, this.currentCaretPosition);
@@ -3066,6 +3107,10 @@ namespace FourSlashInterface {
             this.DocCommentTemplate(/*expectedText*/ undefined, /*expectedOffset*/ undefined, /*empty*/ true);
         }
 
+        public codeFixAtPosition(expectedText: string, errorCode?: number): void {
+            this.state.verifyCodeFixAtPosition(expectedText, errorCode);
+        }
+
         public navigationBar(json: any) {
             this.state.verifyNavigationBar(json);
         }
diff --git a/src/harness/harnessLanguageService.ts b/src/harness/harnessLanguageService.ts
index d7ed04b627f..d2219c3969d 100644
--- a/src/harness/harnessLanguageService.ts
+++ b/src/harness/harnessLanguageService.ts
@@ -453,6 +453,9 @@ namespace Harness.LanguageService {
         isValidBraceCompletionAtPosition(fileName: string, position: number, openingBrace: number): boolean {
             return unwrapJSONCallResult(this.shim.isValidBraceCompletionAtPosition(fileName, position, openingBrace));
         }
+        getCodeFixesAtPosition(fileName: string, start: number, end: number, errorCodes: string[]): ts.CodeAction[] {
+            return unwrapJSONCallResult(this.shim.getCodeFixesAtPosition(fileName, start, end, JSON.stringify(errorCodes)));
+        }
         getEmitOutput(fileName: string): ts.EmitOutput {
             return unwrapJSONCallResult(this.shim.getEmitOutput(fileName));
         }
diff --git a/src/server/client.ts b/src/server/client.ts
index f04dbd8dc02..3c8a07c8cdf 100644
--- a/src/server/client.ts
+++ b/src/server/client.ts
@@ -592,6 +592,10 @@ namespace ts.server {
             throw new Error("Not Implemented Yet.");
         }
 
+        getCodeFixesAtPosition(fileName: string, start: number, end: number, errorCodes: string[]): ts.CodeAction[] {
+            throw new Error("Not Implemented Yet.");
+        }
+
         getBraceMatchingAtPosition(fileName: string, position: number): TextSpan[] {
             const lineOffset = this.positionToOneBasedLineOffset(fileName, position);
             const args: protocol.FileLocationRequestArgs = {
diff --git a/tests/cases/fourslash/fourslash.ts b/tests/cases/fourslash/fourslash.ts
index 9ce3197a46f..ee0d4d100d3 100644
--- a/tests/cases/fourslash/fourslash.ts
+++ b/tests/cases/fourslash/fourslash.ts
@@ -192,6 +192,7 @@ declare namespace FourSlashInterface {
         noMatchingBracePositionInCurrentFile(bracePosition: number): void;
         DocCommentTemplate(expectedText: string, expectedOffset: number, empty?: boolean): void;
         noDocCommentTemplate(): void;
+        codeFixAtPosition(expectedText: string, errorCode?: number): void;
 
         navigationBar(json: any): void;
         navigationItemsListCount(count: number, searchValue: string, matchKind?: string): void;