test: add tests for run_cmd function using echo command

tests/basic/test_run_cmd.py

@@ -0,0 +1,23 @@
+import pytest
+from aider.run_cmd import run_cmd
+
+def test_run_cmd_echo():
+    command = 'echo Hello, World!'
+    exit_code, output = run_cmd(command)
+    
+    assert exit_code == 0
+    assert output.strip() == 'Hello, World!'
+
+def test_run_cmd_echo_with_quotes():
+    command = 'echo "Hello, World!"'
+    exit_code, output = run_cmd(command)
+    
+    assert exit_code == 0
+    assert output.strip() == 'Hello, World!'
+
+def test_run_cmd_invalid_command():
+    command = 'invalid_command_that_does_not_exist'
+    exit_code, output = run_cmd(command)
+    
+    assert exit_code != 0
+    assert 'command not found' in output.lower() or 'is not recognized' in output.lower()