project_1_yaml = {
    'common': {
        'sources': ['sources/main.cpp'],
        'includes': ['includes/header1.h'],
        'target': ['mbed-lpc1768'],
        'linker_file': ['linker_script'],
    }
}

projects_1_yaml = {
    'projects': {
        'project_1' : ['test_workspace/project_1.yaml']
    },
}

project_1_yaml = {
    'common': {
        'sources': ['sources/main.cpp'],
        'includes': ['includes/header1.h'],
        'target': ['mbed-lpc1768']
    }
}

projects_1_yaml = {
    'projects': {
        'project_1' : ['test_workspace/project_1.yaml']
    },
}

--- 
+++ 
@@ -2,7 +2,8 @@
     'common': {
         'sources': ['sources/main.cpp'],
         'includes': ['includes/header1.h'],
-        'target': ['mbed-lpc1768']
+        'target': ['mbed-lpc1768'],
+        'linker_file': ['linker_script'],
     }
 }
 
Test - add linker script for tools project
