Improve README a for hardware specific tests, and make fixes to picamera_tests script

hardware-specific-tests/README.md

@@ -12,7 +12,7 @@ However, this will not archive the tests in the Git repository for reporting the
 
 When writing and debugging these unit tests it is often best to run a specific test and to use the `-s` flag to see the print statements. It is also often useful to use `--pdb` to drop you into a python debug session on any failure. For example, you might run:
 
-    /picamera2/test_exposure_time_drift.py::test_exposure_time_saves_and_loads -s --pdb
+    pytest hardware-specific-tests/picamera2/test_exposure_time_drift.py::test_exposure_time_saves_and_loads -s --pdb
 
 ### Reporting the coverage
 
@@ -20,4 +20,28 @@ To create a coverage report that will be included into the repository run:
 
     ./picamera_tests.py run
 
-This will create a zip of test results along with hashes of the picamera files and the base camera file. The server will include this overage report if the source files remain the same.
+This will create a zip of test results along with hashes of the picamera files and the base camera file. The server will include this coverage report if the source files remain the same.
+
+### Creating a combined report locally
+
+To create a combined coverage report locally (similar to the one created on CI) first run all normal tests with `pytest`.
+
+Copy the `.coverage` file to `.coverage.main`
+
+    cp .coverage .coverage.main
+
+Then run:
+
+    ./picamera_tests.py unzip
+
+to get the `.coverage.picamera` file.
+
+To combine reports run:
+
+    coverage combine
+
+It is then possible to run:
+
+* `coverage report` to get the in-terminal report of the coverage.
+* `coverage html` to get the HTML overview of covered lines.
+* `coverage xml` to get an XML report any software that may need it.

picamera_tests.py

@@ -38,7 +38,7 @@ def _get_hashes(include_coverage: bool = False) -> dict[str, str]:
     filepaths = HASHED_FILES
     if include_coverage:
         filepaths.append(COVERAGE_FILE)
-    for filepath in HASHED_FILES:
+    for filepath in filepaths:
         if not os.path.isfile(filepath):
             # Sys exit rather than raise for better command line experience
             print(f"ERROR: {filepath} does not exist!")