[lldb][tests] Automatically call compute_mydir (NFC)

Eliminate boilerplate of having each test manually assign to `mydir` by calling
`compute_mydir` in lldbtest.py.

Differential Revision: https://reviews.llvm.org/D128077

Author: kastiglione

lldb/packages/Python/lldbsuite/test/README-TestSuite

@@ -4,10 +4,6 @@
 The concrete subclass can override lldbtest.TestBase in order to inherit the
 common behavior for unitest.TestCase.setUp/tearDown implemented in this file.
 
-The subclass should override the attribute mydir in order for the python runtime
-to locate the individual test cases when running as part of a large test suite
-or when running each test case as a separate python invocation.
-
 ./dotest.py provides a test driver which sets up the environment to run the
 entire of part of the test suite .  Example:
 
@@ -539,7 +535,9 @@ def setUpClass(cls):
         Do current directory manipulation.
         """
         # Fail fast if 'mydir' attribute is not overridden.
-        if not cls.mydir or len(cls.mydir) == 0:
+        if not cls.mydir:
+            cls.mydir = Base.compute_mydir(sys.modules[cls.__module__].__file__)
+        if not cls.mydir:
             raise Exception("Subclasses must override the 'mydir' attribute.")
 
         # Save old working directory.
@@ -1703,11 +1701,6 @@ class TestBase(Base):
 
     Important things for test class writers:
 
-        - Overwrite the mydir class attribute, otherwise your test class won't
-          run.  It specifies the relative directory to the top level 'test' so
-          the test harness can change to the correct working directory before
-          running your test.
-
         - The setUp method sets up things to facilitate subsequent interactions
           with the debugger as part of the test.  These include:
               - populate the test method name

lldb/packages/Python/lldbsuite/test/lldbtest.py

@@ -11,8 +11,6 @@
 
 
 class DefaultCacheLineSizeTestCase(TestBase):
-
-    mydir = TestBase.compute_mydir(__file__)
     NO_DEBUG_INFO_TESTCASE = True
 
     @skipUnlessTargetAndroid

lldb/test/API/android/platform/TestDefaultCacheLineSize.py

@@ -12,8 +12,6 @@
 
 
 class SBDirCheckerCase(TestBase):
-
-    mydir = TestBase.compute_mydir(__file__)
     NO_DEBUG_INFO_TESTCASE = True
 
     def setUp(self):

lldb/test/API/api/check_public_api_headers/TestPublicAPIHeaders.py

@@ -9,8 +9,6 @@
 
 
 class TestSBCommandReturnObject(TestBase):
-
-    mydir = TestBase.compute_mydir(__file__)
     NO_DEBUG_INFO_TESTCASE = True
 
     @skipIfNoSBHeaders

lldb/test/API/api/command-return-object/TestSBCommandReturnObject.py

@@ -10,8 +10,6 @@
 import six
 
 class ListenToModuleLoadedEvents (TestBase):
-
-    mydir = TestBase.compute_mydir(__file__)
     NO_DEBUG_INFO_TESTCASE = True
 
     def test_clearing_listener(self):

lldb/test/API/api/listeners/TestListener.py

@@ -11,8 +11,6 @@
 
 class APILogTestCase(TestBase):
 
-    mydir = TestBase.compute_mydir(__file__)
-
     NO_DEBUG_INFO_TESTCASE = True
 
     def test_api_log(self):

lldb/test/API/api/log/TestAPILog.py

@@ -13,8 +13,6 @@
 
 class TestMultipleSimultaneousDebuggers(TestBase):
 
-    mydir = TestBase.compute_mydir(__file__)
-
     NO_DEBUG_INFO_TESTCASE = True
 
     @skipIfNoSBHeaders

lldb/test/API/api/multiple-debuggers/TestMultipleDebuggers.py

@@ -12,8 +12,6 @@
 
 
 class TestMultipleTargets(TestBase):
-
-    mydir = TestBase.compute_mydir(__file__)
     NO_DEBUG_INFO_TESTCASE = True
 
     @skipIf(oslist=["linux"], archs=["arm", "aarch64"])

lldb/test/API/api/multiple-targets/TestMultipleTargets.py

@@ -25,8 +25,6 @@ def setUp(self):
         self.generateSource('test_listener_resume.cpp')
         self.generateSource('test_stop-hook.cpp')
 
-    mydir = TestBase.compute_mydir(__file__)
-
     @skipIfRemote
     @skipIfNoSBHeaders
     # clang-cl does not support throw or catch (llvm.org/pr24538)