Move test_methodCallTypeInference_mixinType into mixin_test.dart

Addresses code review comments on https://dart-review.googlesource.com/c/sdk/+/81322.

Change-Id: I8c8bd20f024a849042ff862f755a4187765f6201
Reviewed-on: https://dart-review.googlesource.com/c/81330
Commit-Queue: Paul Berry <paulberry@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>
Auto-Submit: Paul Berry <paulberry@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>

pkg/analyzer/test/generated/non_error_resolver_test.dart

@@ -3655,29 +3655,6 @@ enum E {
     verify([source]);
   }
 
-  test_methodCallTypeInference_mixinType() async {
-    Source source = addSource('''
-main() {
-  C<int> c = f();
-}
-
-class C<T> {}
-
-mixin M<T> on C<T> {}
-
-M<T> f<T>() => null;
-''');
-    var result = await computeAnalysisResult(source);
-    assertNoErrors(source);
-    verify([source]);
-    var main = result.unit.declarations[0] as FunctionDeclaration;
-    var body = main.functionExpression.body as BlockFunctionBody;
-    var cDeclaration = body.block.statements[0] as VariableDeclarationStatement;
-    var fInvocation =
-        cDeclaration.variables.variables[0].initializer as MethodInvocation;
-    expect(fInvocation.staticInvokeType.toString(), '() → M<int>');
-  }
-
   test_methodDeclaration_scope_signature() async {
     Source source = addSource(r'''
 const app = 0;

pkg/analyzer/test/src/dart/resolution/mixin_test.dart

@@ -2,6 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/src/dart/error/syntactic_errors.dart';
 import 'package:analyzer/src/error/codes.dart';
@@ -1693,6 +1694,24 @@ mixin M {}
     expect(annotation.elementAnnotation, same(metadata[0]));
   }
 
+  test_methodCallTypeInference_mixinType() async {
+    addTestFile('''
+main() {
+  C<int> c = f();
+}
+
+class C<T> {}
+
+mixin M<T> on C<T> {}
+
+M<T> f<T>() => null;
+''');
+    await resolveTestFile();
+    assertNoTestErrors();
+    var fInvocation = findNode.methodInvocation('f()');
+    expect(fInvocation.staticInvokeType.toString(), '() → M<int>');
+  }
+
   test_onClause() async {
     addTestFile(r'''
 class A {}