fix: returns validation error on unknown combination of real/expected…

… body content types

lib/next/test/unit/units/validateBody.test.js

@@ -19,6 +19,49 @@ describe('validateBody', () => {
   });
 
   describe('when given supported body type', () => {
+    describe('in a combination without related validator', () => {
+      const result = validateBody(
+        {
+          headers: { 'content-type': 'application/json' },
+          body: '{ "foo": "bar" }'
+        },
+        {
+          headers: { 'content-type': 'text/plain' },
+          body: ''
+        }
+      );
+
+      it('has no validator', () => {
+        assert.isNull(result.validator);
+      });
+
+      it('has "application/json" real type', () => {
+        assert.propertyVal(result, 'realType', 'application/json');
+      });
+
+      it('has "text/plain" expected type', () => {
+        assert.propertyVal(result, 'expectedType', 'text/plain');
+      });
+
+      describe('produces validation error', () => {
+        it('exactly one error', () => {
+          assert.lengthOf(result.results, 1);
+        });
+
+        it('has "error" severity', () => {
+          assert.propertyVal(result.results[0], 'severity', 'error');
+        });
+
+        it('has explanatory message', () => {
+          assert.propertyVal(
+            result.results[0],
+            'message',
+            `Can't validate real media type 'application/json' against expected media type 'text/plain'.`
+          );
+        });
+      });
+    });
+
     describe('with explicit "Content-Type" header', () => {
       describe('application/json', () => {
         describe('with matching body type', () => {

lib/next/units/validateBody.js

@@ -141,6 +141,13 @@ function getBodyValidator(realType, expectedType) {
     return predicate(realType, expectedType);
   });
 
+  if (!validator) {
+    const error = `Can't validate real media type '${mediaTyper.format(
+      realType
+    )}' against expected media type '${mediaTyper.format(expectedType)}'.`;
+    return [error, null];
+  }
+
   return [null, validator[0]];
 }