fix unit tests for running on the ESP32 device

When running unit tests on the ESP32, the current directory is root, while
on the PC (or in the GitHub Actions), the tests/ directory is the current
directory. Unit tests that rely on fixture files fails because of this.
Now test scripts can look for fixture files relative to their own path to
make them independent of the current directory.

Author: wnienhaus

tests/preprocess.py

@@ -11,6 +11,21 @@ def test(param):
     tests.append(param)
 
 
+def resolve_relative_path(filename):
+    """
+    Returns the full path to the filename provided, taken relative to the current file
+    e.g.
+      if this file was file.py at /path/to/file.py
+      and the provided relative filename was tests/unit.py
+      then the resulting path would be /path/to/tests/unit.py
+    """
+    r = __file__.rsplit("/", 1)  # poor man's os.path.dirname(__file__)
+    head = r[0]
+    if len(r) == 1 or not head:
+        return filename
+    return "%s/%s" % (head, filename)
+
+
 @test
 def test_replace_defines_should_return_empty_line_given_empty_string():
     p = Preprocessor()
@@ -204,7 +219,7 @@ def preprocess_should_replace_BIT_with_empty_string_unless_defined():
 def test_process_include_file():
     p = Preprocessor()
 
-    defines = p.process_include_file('fixtures/incl.h')
+    defines = p.process_include_file(resolve_relative_path('fixtures/incl.h'))
 
     assert defines['CONST1'] == '42'
     assert defines['CONST2'] == '99'
@@ -216,8 +231,8 @@ def test_process_include_file():
 def test_process_include_file_with_multiple_files():
     p = Preprocessor()
 
-    defines = p.process_include_file('fixtures/incl.h')
-    defines = p.process_include_file('fixtures/incl2.h')
+    defines = p.process_include_file(resolve_relative_path('fixtures/incl.h'))
+    defines = p.process_include_file(resolve_relative_path('fixtures/incl2.h'))
 
     assert defines['CONST1'] == '42', "constant from incl.h"
     assert defines['CONST2'] == '123', "constant overridden by incl2.h"
@@ -232,8 +247,8 @@ def test_process_include_file_using_database():
     p = Preprocessor()
     p.use_db(db)
 
-    p.process_include_file('fixtures/incl.h')
-    p.process_include_file('fixtures/incl2.h')
+    p.process_include_file(resolve_relative_path('fixtures/incl.h'))
+    p.process_include_file(resolve_relative_path('fixtures/incl2.h'))
 
     assert db['CONST1'] == '42', "constant from incl.h"
     assert db['CONST2'] == '123', "constant overridden by incl2.h"
@@ -250,7 +265,7 @@ def test_process_include_file_should_not_load_database_keys_into_instance_define
     p = Preprocessor()
     p.use_db(db)
 
-    p.process_include_file('fixtures/incl.h')
+    p.process_include_file(resolve_relative_path('fixtures/incl.h'))
 
     # a bit hackish to reference instance-internal state
     # but it's important to verify this, as we otherwise run out of memory on device