add test for undefined variable environment file import

test to show current behavior is wrong at parsing an environment file
defining an undefined variable - it must not be defined!

NOTE: this test assume the $HOME variable is always set (see POSIX, this
      normally is the case, e.g. the test suite remains stable).

Signed-off-by: Tom Klingenberg <tklingenberg@lastflood.net>

opts/envfile_test.go

@@ -139,3 +139,26 @@ another invalid line`
 		t.Fatalf("Expected [%v], got [%v]", expectedMessage, err.Error())
 	}
 }
+
+// ParseEnvFile with environment variable import definitions
+func TestParseEnvVariableDefinitionsFile(t *testing.T) {
+	content := `# comment=
+UNDEFINED_VAR
+HOME
+`
+	tmpFile := tmpFileWithContent(content, t)
+	defer os.Remove(tmpFile)
+
+	variables, err := ParseEnvFile(tmpFile)
+	if nil != err {
+		t.Fatal("There must not be any error")
+	}
+
+	if "HOME="+os.Getenv("HOME") != variables[0] {
+		t.Fatal("the HOME variable is not properly imported as the first variable (but it is the only one to import)")
+	}
+
+	if 1 != len(variables) {
+		t.Fatal("exactly one variable is imported (as the other one is not set at all)")
+	}
+}