PY-26102: Suggest test runner for any file starting with "test_"

Any file that starts with "test_" may be used as pytest/nosetest target
regardless its content.
Unittest is skipped because of "testCaseClassRequired".

python/src/com/jetbrains/python/testing/PythonUnitTestUtil.java

@@ -74,7 +74,8 @@ public final class PythonUnitTestUtil {
     if (isTestCaseClassRequired(file, testCaseClassRequired)) {
       return false;
     }
-    return file.getTopLevelFunctions().stream().anyMatch(o -> isTestFunction(o, testCaseClassRequired, context));
+    return file.getName().startsWith("test_") ||
+           file.getTopLevelFunctions().stream().anyMatch(o -> isTestFunction(o, testCaseClassRequired, context));
   }
 
   /**

python/testSrc/com/jetbrains/env/python/testing/CreateConfigurationMultipleCasesTask.java

@@ -52,6 +52,7 @@ class CreateConfigurationMultipleCasesTask<T extends PyAbstractTestConfiguration
 
     result.add(getDir("tests_package/package_test"));
     result.add(getFile("tests_package/package_test", "test_in_package.py"));
+    result.add(getFile("/", "test_foo.py"));
     result.add(getFile("tests_package/package_test", "test_in_package.py").findTopLevelClass("TestLogic"));
 
     result.add(getDir("tests_folder"));
@@ -123,6 +124,9 @@ class CreateConfigurationMultipleCasesTask<T extends PyAbstractTestConfiguration
     else if (element instanceof PyFunction && elementName.endsWith("foo")) {
       Assert.assertEquals("non-test function should lead to level-based test", TestTargetType.PATH, target.getTargetType());
     }
+    else if (element instanceof PyFile && elementName.endsWith("test_foo.py")) {
+      Assert.assertEquals("Wrong path for file-based target", TestTargetType.PATH, target.getTargetType());
+    }
     else {
       throw new AssertionError("Unexpected configuration " + configuration);
     }
@@ -141,7 +145,7 @@ class CreateConfigurationMultipleCasesTask<T extends PyAbstractTestConfiguration
   @NotNull
   private PyFile getFile(@NotNull final String dirName, @NotNull final String fileName) {
     final PsiFile psiFile = getDir(dirName).findFile(fileName);
-    assert psiFile instanceof PyFile : "Bad file " + psiFile;
+    assert psiFile instanceof PyFile : "Bad file " + psiFile + "name: " + fileName;
     return (PyFile)psiFile;
   }
 }

python/testSrc/com/jetbrains/env/python/testing/PythonUnitTestingTest.java

@@ -666,9 +666,13 @@ public final class PythonUnitTestingTest extends PythonUnitTestingLikeTest<PyUni
                                                                         PyUnitTestConfiguration.class) {
         @Override
         protected boolean configurationShouldBeProducedForElement(@NotNull final PsiElement element) {
-          // test_functions.py does not conttain any TestCase and can't be launched with unittest
+          // test_functions.py and test_foo do not contain any TestCase and can't be launched with unittest
           final PsiFile file = element.getContainingFile();
-          return file == null || !file.getName().endsWith("test_functions.py");
+          if (file == null) {
+            return true;
+          }
+          final String name = file.getName();
+          return !(name.endsWith("test_functions.py") || name.endsWith("test_foo.py"));
         }
       });
   }