Add subcommand read, for acquiring and displaying a reading on STDOUT

... in JSON format.

CHANGES.md

@@ -8,6 +8,7 @@
   The data logger uses a YAML file now, for example like `etc/mois.yaml`.
 - Added subcommand `make-config`, for creating a configuration blueprint
 - Added subcommand `make-dashboard`, for creating a Grafana Dashboard
+- Added subcommand `read`, for acquiring and displaying a reading on STDOUT
 
 ## v0.0.2 - 2024-04-15
 - Publish as `ds18b20-datalogger` package

ds18b20_datalogger/cli.py

@@ -1,3 +1,4 @@
+import json
 import sys
 from pathlib import Path
 
@@ -11,23 +12,33 @@
 
 
 def main():
+
+    # Sanity checks.
     if not sys.argv[1:]:
         raise ValueError("Program needs a subcommand")
     subcommand = sys.argv[1]
-    if subcommand == "run":
+
+    # Evaluate subcommand.
+    if subcommand in ["run", "read"]:
         if not sys.argv[2:]:
             raise ValueError("Program needs a configuration file")
         configfile = Path(sys.argv[2])
         if not configfile.exists():
             raise ValueError(f"Configuration file does not exist: {configfile}")
         settings = Settings.from_file(configfile)
         reading = read_ds18b20_sensor_matrix(settings.devicemap)
-        send_measurement_mqtt(settings.mqtt, reading)
+        if subcommand == "read":
+            print(json.dumps(reading.to_dict(), indent=2))  # noqa: T201
+        elif subcommand == "run":
+            send_measurement_mqtt(settings.mqtt, reading)
+
     elif subcommand == "make-config":
         config_template = files("ds18b20_datalogger") / "datalogger.yaml"
         print(config_template.read_text(), file=sys.stdout)  # noqa: T201
+
     elif subcommand == "make-dashboard":
         dashboard = files("ds18b20_datalogger") / "grafana-dashboard.json"
         print(dashboard.read_text(), file=sys.stdout)  # noqa: T201
+
     else:
         raise ValueError(f"Subcommand unknown: {subcommand}")

tests/test_cli.py

@@ -1,4 +1,5 @@
 import json
+import shlex
 import subprocess
 import typing as t
 
@@ -19,10 +20,28 @@ def test_cli_unknown_subcommand():
     assert "Subcommand unknown: foo" in output
 
 
-def test_cli_run_no_config():
+def test_cli_run_read_no_config():
     exitcode, output = invoke("ds18b20-datalogger run")
     assert "Program needs a configuration file" in output
 
+    exitcode, output = invoke("ds18b20-datalogger read")
+    assert "Program needs a configuration file" in output
+
+
+def test_cli_read_success():
+    command = shlex.split("ds18b20-datalogger read ds18b20_datalogger/datalogger.yaml")
+    process = subprocess.run(command, stdout=subprocess.PIPE)  # noqa: S603
+    reading = json.loads(process.stdout)
+    assert "temp-ir-1-1" in reading
+    assert "temp-ir-2-3" in reading
+    assert len(reading) == 6
+
+
+def test_cli_run_almost_success():
+    exitcode, output = invoke("ds18b20-datalogger run ds18b20_datalogger/datalogger.yaml")
+    assert exitcode == 1
+    assert "nodename nor servname provided, or not known" in output
+
 
 def test_cli_make_config():
     exitcode, output = invoke("ds18b20-datalogger make-config")