More coverage

Author: MilesCranmer

README.md

@@ -243,7 +243,19 @@ julia> using DynamicQuantities.SymbolicConstants: h
 
 Note that `SymbolicUnits` and `SymbolicConstants` are exported,
 so you can simply access these as `SymbolicUnits.cm` and `SymbolicConstants.h`,
-respectively.
+respectively. I like to work with these like so:
+
+```julia
+julia> const u = DynamicQuantities.SymbolicUnits;
+
+julia> const C = DynamicQuantities.SymbolicConstants;
+```
+
+so that I can simply write things like:
+
+```julia
+julia> u.yr * C.c |> uexpand |> uconvert(u.km)
+```
 
 
 ### Arrays

docs/src/types.md

@@ -25,6 +25,17 @@ Another type which subtypes `AbstractDimensions` is `SymbolicDimensions`:
 SymbolicDimensions
 ```
 
+Just note that all of the symbolic units and constants are stored using the
+immutable `SymbolicDimensionsSingleton`, which shares the same
+supertype `AbstractSymbolicDimensions <: SymbolicDimensions`. These get immediately
+converted to the mutable `SymbolicDimensions` when used in any
+calculation.
+
+```@docs
+SymbolicDimensionsSingleton
+AbstractSymbolicDimensions
+```
+
 ## Arrays
 
 ```@docs

test/unittests.jl

@@ -1681,6 +1681,7 @@ end
 
 @testset "Tests of SymbolicDimensionsSingleton" begin
     km = SymbolicUnits.km
+    m = SymbolicUnits.m
     @test km isa Quantity{T,SymbolicDimensionsSingleton{R}} where {T,R}
     @test dimension(km) isa SymbolicDimensionsSingleton
     @test dimension(km) isa AbstractSymbolicDimensions
@@ -1730,6 +1731,19 @@ end
             SymbolicDimensionsSingleton{Int64},
             Dimensions{Int16}
         ) === Dimensions{Int64}
+
+    # Test map_dimensions explicitly for coverage:
+    @test map_dimensions(-, dimension(km)).km == -1
+    @test map_dimensions(-, dimension(km)) isa SymbolicDimensions
+    @test map_dimensions(+, dimension(km), dimension(m)).km == 1
+    @test map_dimensions(+, dimension(km), dimension(m)).m == 1
+    @test map_dimensions(+, dimension(km), dimension(m)).cm == 0
+    @test map_dimensions(+, dimension(km), SymbolicDimensions(dimension(m))).km == 1
+    @test map_dimensions(+, dimension(km), SymbolicDimensions(dimension(m))).m == 1
+    @test map_dimensions(+, dimension(km), SymbolicDimensions(dimension(m))).cm == 0
+    @test map_dimensions(+, SymbolicDimensions(dimension(km)), dimension(m)).km == 1
+    @test map_dimensions(+, SymbolicDimensions(dimension(km)), dimension(m)).m == 1
+    @test map_dimensions(+, SymbolicDimensions(dimension(km)), dimension(m)).cm == 0
 end
 
 @testset "Test div" begin