diff --git a/src/generate-method-id.ts b/src/generate-method-id.ts
index f897f905..1effa108 100644
--- a/src/generate-method-id.ts
+++ b/src/generate-method-id.ts
@@ -5,19 +5,20 @@ import { MethodObject, ContentDescriptorObject } from "@open-rpc/meta-schema";
  * Provides an error interface for handling when we are unable to find a contentDescriptor in a methodObject
  * when it is expected.
  */
-export class ContentDescriptorNotFoundInMethodError extends Error {
+export class ContentDescriptorNotFoundInMethodError implements Error {
+  public name = "OpenRPCDocumentDereferencingError";
+  public message: string;
 
   /**
    * @param method OpenRPC Method which was used for the lookup
    * @param contentDescriptor OpenRPC Content Descriptor that was expected to be in the method param.
    */
   constructor(public method: MethodObject, public contentDescriptor: ContentDescriptorObject) {
-    /* istanbul ignore next */
-    super([
+    this.message = [
       "Content Descriptor not found in method.",
       `Method: ${JSON.stringify(method, undefined, "  ")}`,
       `ContentDescriptor: ${JSON.stringify(contentDescriptor, undefined, "  ")}`,
-    ].join("\n")) /* istanbul ignore next */;
+    ].join("\n");
   }
 }
 
diff --git a/src/method-call-validator/method-call-validator.test.ts b/src/method-call-validator/method-call-validator.test.ts
index 07f10798..a63f4c5b 100644
--- a/src/method-call-validator/method-call-validator.test.ts
+++ b/src/method-call-validator/method-call-validator.test.ts
@@ -1,5 +1,6 @@
 import MethodCallValidator from "./method-call-validator";
 import { OpenRPC } from "@open-rpc/meta-schema";
+import MethodCallParameterValidationError from "./parameter-validation-error";
 
 const getExampleSchema = (): OpenRPC => ({
   info: { title: "123", version: "1" },
@@ -47,7 +48,7 @@ describe("MethodCallValidator", () => {
     const methodCallValidator = new MethodCallValidator(example);
     const result = methodCallValidator.validate("foo", [123]);
     expect(result.length).toBe(1);
-    expect(result[0]).toBeInstanceOf(Error);
+    expect(result[0]).toBeInstanceOf(MethodCallParameterValidationError);
   });
 
 });
diff --git a/src/method-call-validator/parameter-validation-error.test.ts b/src/method-call-validator/parameter-validation-error.test.ts
index e88a8315..9b002102 100644
--- a/src/method-call-validator/parameter-validation-error.test.ts
+++ b/src/method-call-validator/parameter-validation-error.test.ts
@@ -1,5 +1,6 @@
 import ParameterValidationError from "./parameter-validation-error";
 import { ErrorObject } from "ajv";
+import MethodCallParameterValidationError from "./parameter-validation-error";
 
 describe("ParameterValidationError", () => {
   const errorObj = {
@@ -11,6 +12,6 @@ describe("ParameterValidationError", () => {
 
   it("can be instantiated", () => {
     const error = new ParameterValidationError(1, { type: "number" }, "hey mom", [errorObj]);
-    expect(error).toBeInstanceOf(Error);
+    expect(error).toBeInstanceOf(MethodCallParameterValidationError);
   });
 });
diff --git a/src/method-call-validator/parameter-validation-error.ts b/src/method-call-validator/parameter-validation-error.ts
index a42d2bb6..b4412f1a 100644
--- a/src/method-call-validator/parameter-validation-error.ts
+++ b/src/method-call-validator/parameter-validation-error.ts
@@ -4,7 +4,9 @@ import { Schema } from "@open-rpc/meta-schema";
 /**
  * Provides an error interface for handling when a function call has invalid parameters.
  */
-export default class MethodCallParameterValidationError extends Error {
+export default class MethodCallParameterValidationError implements Error {
+  public name = "OpenRPCDocumentDereferencingError";
+  public message: string;
 
   /**
    * @param paramIndex The index of the param that for this error (index
@@ -19,7 +21,7 @@ export default class MethodCallParameterValidationError extends Error {
     public receievedParam: any,
     private errors: ErrorObject[],
   ) {
-    super([
+    this.message = [
       "Expected param in position ",
       paramIndex,
       " to match the json schema: ",
@@ -27,6 +29,6 @@ export default class MethodCallParameterValidationError extends Error {
       ". The function received instead ",
       receievedParam,
       ".",
-    ].join("")) /* istanbul ignore next */;
+    ].join("");
   }
 }
diff --git a/src/parse-open-rpc-document.test.ts b/src/parse-open-rpc-document.test.ts
index 668407b8..fdbd14a8 100644
--- a/src/parse-open-rpc-document.test.ts
+++ b/src/parse-open-rpc-document.test.ts
@@ -4,8 +4,9 @@ jest.mock("fs-extra", () => ({
 }));
 
 import * as _fs from "fs-extra";
-import parseOpenRPCDocument from "./parse-open-rpc-document";
+import parseOpenRPCDocument, { OpenRPCDocumentDereferencingError } from "./parse-open-rpc-document";
 import { OpenRPC } from "@open-rpc/meta-schema";
+import { OpenRPCDocumentValidationError } from "./validate-open-rpc-document";
 
 const fs: any = _fs;
 
@@ -82,8 +83,7 @@ describe("parseOpenRPCDocument", () => {
 
     it("rejects when the schema cannot be dereferenced", () => {
       expect.assertions(1);
-      fs.readJson.mockClear();
-      fs.readJson.mockResolvedValue({
+      const testDocument = {
         ...workingSchema,
         methods: [
           {
@@ -100,16 +100,16 @@ describe("parseOpenRPCDocument", () => {
             },
           },
         ],
-      });
-      return expect(parseOpenRPCDocument())
+      };
+
+      return expect(parseOpenRPCDocument(testDocument))
         .rejects
-        .toThrow("The json schema provided cannot be dereferenced");
+        .toBeInstanceOf(OpenRPCDocumentDereferencingError);
     });
 
     it("rejects when the schema is invalid", () => {
       expect.assertions(1);
-      fs.readJson.mockClear();
-      fs.readJson.mockResolvedValue({
+      const testDocument = {
         ...workingSchema,
         methods: [
           {
@@ -127,10 +127,10 @@ describe("parseOpenRPCDocument", () => {
             zfloobars: 123,
           },
         ],
-      });
-      return expect(parseOpenRPCDocument())
+      };
+      return expect(parseOpenRPCDocument(testDocument))
         .rejects
-        .toThrow(/Error validating OpenRPC Document against @open-rpc\/meta-schema./);
+        .toBeInstanceOf(OpenRPCDocumentValidationError);
     });
 
     it("rejects when the json provided is invalid from file", () => {
diff --git a/src/parse-open-rpc-document.ts b/src/parse-open-rpc-document.ts
index 57675d73..6a29aebd 100644
--- a/src/parse-open-rpc-document.ts
+++ b/src/parse-open-rpc-document.ts
@@ -20,14 +20,15 @@ const isJson = (jsonString: string) => {
 /**
  * Provides an error interface for OpenRPC Document dereferencing problems
  */
-export class OpenRPCDocumentDereferencingError extends Error {
+export class OpenRPCDocumentDereferencingError implements Error {
+  public name = "OpenRPCDocumentDereferencingError";
+  public message: string;
 
   /**
    * @param e The error that originated from jsonSchemaRefParser
    */
   constructor(e: Error) {
-    /* istanbul ignore next */
-    super(`The json schema provided cannot be dereferenced. Received Error: \n ${e.message}`);
+    this.message = `The json schema provided cannot be dereferenced. Received Error: \n ${e.message}`;
   }
 }
 
diff --git a/src/validate-open-rpc-document.ts b/src/validate-open-rpc-document.ts
index 01258f7b..4475eba1 100644
--- a/src/validate-open-rpc-document.ts
+++ b/src/validate-open-rpc-document.ts
@@ -11,17 +11,19 @@ ajv.addMetaSchema(JsonSchemaDraft07, "https://json-schema.org/draft-07/schema#")
 /**
  * Provides an error interface for OpenRPC Document validation
  */
-export class OpenRPCDocumentValidationError extends Error {
+export class OpenRPCDocumentValidationError implements Error {
+  public name = "OpenRPCDocumentDereferencingError";
+  public message: string;
 
   /**
    * @param errors The errors received by ajv.errors.
    */
   constructor(private errors: ErrorObject[]) {
-    super([
+    this.message = [
       "Error validating OpenRPC Document against @open-rpc/meta-schema.",
       "The errors found are as follows:",
       JSON.stringify(errors, undefined, "  "),
-    ].join("\n")) /* istanbul ignore next */;
+    ].join("\n");
   }
 }