Refactor test cases for improved readability and consistency

- Updated test functions in various test files to enhance code clarity by formatting long lines and improving indentation.
- Adjusted assertions to use multi-line formatting for better readability.
- Added new test cases for theme settings API to ensure proper functionality.
- Ensured consistent use of line breaks and spacing across test files for uniformity.

models/currency.py

@@ -14,8 +14,11 @@ class Currency(Base):
 
     # reverse relationships (optional)
     capex_items = relationship(
-        "Capex", back_populates="currency", lazy="select")
+        "Capex", back_populates="currency", lazy="select"
+    )
     opex_items = relationship("Opex", back_populates="currency", lazy="select")
 
     def __repr__(self):
-        return f"<Currency code={self.code} name={self.name} symbol={self.symbol}>"
+        return (
+            f"<Currency code={self.code} name={self.name} symbol={self.symbol}>"
+        )