Add a lot of test coverage

7 files changed, 872 insertions, 21 deletions

diff --git a/.gitignore b/.gitignore
index 04c01ba..94934f9 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,3 @@
 node_modules/
-dist/
\ No newline at end of file
+dist/
+coverage/
\ No newline at end of file
diff --git a/index.js b/index.js
deleted file mode 100644
index 56004c9..0000000
--- a/index.js
+++ /dev/null
@@ -1 +0,0 @@
-export default {}
\ No newline at end of file
diff --git a/package-lock.json b/package-lock.json
index 85c2e1d..33ac84e 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,20 +1,304 @@
 {
   "name": "flatmatter",
-  "version": "0.1.0",
+  "version": "0.2.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "flatmatter",
-      "version": "0.1.0",
+      "version": "0.2.0",
       "license": "MIT",
       "devDependencies": {
+        "@vitest/coverage-istanbul": "^2.1.8",
+        "@vitest/coverage-v8": "^2.1.8",
+        "@vitest/ui": "^2.1.8",
         "tsup": "^8.3.5",
         "typescript": "^5.7.3",
         "vite": "^5.4.11",
         "vitest": "^2.1.8"
       }
     },
+    "node_modules/@ampproject/remapping": {
+      "version": "2.3.0",
+      "resolved": "https://registry.npmjs.org/@ampproject/remapping/-/remapping-2.3.0.tgz",
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+      "dev": true,
+      "license": "Apache-2.0",
+      "dependencies": {
+        "@jridgewell/gen-mapping": "^0.3.5",
+        "@jridgewell/trace-mapping": "^0.3.24"
+      },
+      "engines": {
+        "node": ">=6.0.0"
+      }
+    },
+    "node_modules/@babel/code-frame": {
+      "version": "7.26.2",
+      "resolved": "https://registry.npmjs.org/@babel/code-frame/-/code-frame-7.26.2.tgz",
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+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@babel/helper-validator-identifier": "^7.25.9",
+        "js-tokens": "^4.0.0",
+        "picocolors": "^1.0.0"
+      },
+      "engines": {
+        "node": ">=6.9.0"
+      }
+    },
+    "node_modules/@babel/compat-data": {
+      "version": "7.26.5",
+      "resolved": "https://registry.npmjs.org/@babel/compat-data/-/compat-data-7.26.5.tgz",
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+      "dev": true,
+      "license": "MIT",
+      "engines": {
+        "node": ">=6.9.0"
+      }
+    },
+    "node_modules/@babel/core": {
+      "version": "7.26.0",
+      "resolved": "https://registry.npmjs.org/@babel/core/-/core-7.26.0.tgz",
+      "integrity": "sha512-i1SLeK+DzNnQ3LL/CswPCa/E5u4lh1k6IAEphON8F+cXt0t9euTshDru0q7/IqMa1PMPz5RnHuHscF8/ZJsStg==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@ampproject/remapping": "^2.2.0",
+        "@babel/code-frame": "^7.26.0",
+        "@babel/generator": "^7.26.0",
+        "@babel/helper-compilation-targets": "^7.25.9",
+        "@babel/helper-module-transforms": "^7.26.0",
+        "@babel/helpers": "^7.26.0",
+        "@babel/parser": "^7.26.0",
+        "@babel/template": "^7.25.9",
+        "@babel/traverse": "^7.25.9",
+        "@babel/types": "^7.26.0",
+        "convert-source-map": "^2.0.0",
+        "debug": "^4.1.0",
+        "gensync": "^1.0.0-beta.2",
+        "json5": "^2.2.3",
+        "semver": "^6.3.1"
+      },
+      "engines": {
+        "node": ">=6.9.0"
+      },
+      "funding": {
+        "type": "opencollective",
+        "url": "https://opencollective.com/babel"
+      }
+    },
+    "node_modules/@babel/core/node_modules/semver": {
+      "version": "6.3.1",
+      "resolved": "https://registry.npmjs.org/semver/-/semver-6.3.1.tgz",
+      "integrity": "sha512-BR7VvDCVHO+q2xBEWskxS6DJE1qRnb7DxzUrogb71CWoSficBxYsiAGd+Kl0mmq/MprG9yArRkyrQxTO6XjMzA==",
+      "dev": true,
+      "license": "ISC",
+      "bin": {
+        "semver": "bin/semver.js"
+      }
+    },
+    "node_modules/@babel/generator": {
+      "version": "7.26.5",
+      "resolved": "https://registry.npmjs.org/@babel/generator/-/generator-7.26.5.tgz",
+      "integrity": "sha512-2caSP6fN9I7HOe6nqhtft7V4g7/V/gfDsC3Ag4W7kEzzvRGKqiv0pu0HogPiZ3KaVSoNDhUws6IJjDjpfmYIXw==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@babel/parser": "^7.26.5",
+        "@babel/types": "^7.26.5",
+        "@jridgewell/gen-mapping": "^0.3.5",
+        "@jridgewell/trace-mapping": "^0.3.25",
+        "jsesc": "^3.0.2"
+      },
+      "engines": {
+        "node": ">=6.9.0"
+      }
+    },
+    "node_modules/@babel/helper-compilation-targets": {
+      "version": "7.26.5",
+      "resolved": "https://registry.npmjs.org/@babel/helper-compilation-targets/-/helper-compilation-targets-7.26.5.tgz",
+      "integrity": "sha512-IXuyn5EkouFJscIDuFF5EsiSolseme1s0CZB+QxVugqJLYmKdxI1VfIBOst0SUu4rnk2Z7kqTwmoO1lp3HIfnA==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@babel/compat-data": "^7.26.5",
+        "@babel/helper-validator-option": "^7.25.9",
+        "browserslist": "^4.24.0",
+        "lru-cache": "^5.1.1",
+        "semver": "^6.3.1"
+      },
+      "engines": {
+        "node": ">=6.9.0"
+      }
+    },
+    "node_modules/@babel/helper-compilation-targets/node_modules/lru-cache": {
+      "version": "5.1.1",
+      "resolved": "https://registry.npmjs.org/lru-cache/-/lru-cache-5.1.1.tgz",
+      "integrity": "sha512-KpNARQA3Iwv+jTA0utUVVbrh+Jlrr1Fv0e56GGzAFOXN7dk/FviaDW8LHmK52DlcH4WP2n6gI8vN1aesBFgo9w==",
+      "dev": true,
+      "license": "ISC",
+      "dependencies": {
+        "yallist": "^3.0.2"
+      }
+    },
+    "node_modules/@babel/helper-compilation-targets/node_modules/semver": {
+      "version": "6.3.1",
+      "resolved": "https://registry.npmjs.org/semver/-/semver-6.3.1.tgz",
+      "integrity": "sha512-BR7VvDCVHO+q2xBEWskxS6DJE1qRnb7DxzUrogb71CWoSficBxYsiAGd+Kl0mmq/MprG9yArRkyrQxTO6XjMzA==",
+      "dev": true,
+      "license": "ISC",
+      "bin": {
+        "semver": "bin/semver.js"
+      }
+    },
+    "node_modules/@babel/helper-module-imports": {
+      "version": "7.25.9",
+      "resolved": "https://registry.npmjs.org/@babel/helper-module-imports/-/helper-module-imports-7.25.9.tgz",
+      "integrity": "sha512-tnUA4RsrmflIM6W6RFTLFSXITtl0wKjgpnLgXyowocVPrbYrLUXSBXDgTs8BlbmIzIdlBySRQjINYs2BAkiLtw==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@babel/traverse": "^7.25.9",
+        "@babel/types": "^7.25.9"
+      },
+      "engines": {
+        "node": ">=6.9.0"
+      }
+    },
+    "node_modules/@babel/helper-module-transforms": {
+      "version": "7.26.0",
+      "resolved": "https://registry.npmjs.org/@babel/helper-module-transforms/-/helper-module-transforms-7.26.0.tgz",
+      "integrity": "sha512-xO+xu6B5K2czEnQye6BHA7DolFFmS3LB7stHZFaOLb1pAwO1HWLS8fXA+eh0A2yIvltPVmx3eNNDBJA2SLHXFw==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@babel/helper-module-imports": "^7.25.9",
+        "@babel/helper-validator-identifier": "^7.25.9",
+        "@babel/traverse": "^7.25.9"
+      },
+      "engines": {
+        "node": ">=6.9.0"
+      },
+      "peerDependencies": {
+        "@babel/core": "^7.0.0"
+      }
+    },
+    "node_modules/@babel/helper-string-parser": {
+      "version": "7.25.9",
+      "resolved": "https://registry.npmjs.org/@babel/helper-string-parser/-/helper-string-parser-7.25.9.tgz",
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+      "dev": true,
+      "license": "MIT",
+      "engines": {
+        "node": ">=6.9.0"
+      }
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+    "node_modules/@babel/helper-validator-identifier": {
+      "version": "7.25.9",
+      "resolved": "https://registry.npmjs.org/@babel/helper-validator-identifier/-/helper-validator-identifier-7.25.9.tgz",
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+      "dev": true,
+      "license": "MIT",
+      "engines": {
+        "node": ">=6.9.0"
+      }
+    },
+    "node_modules/@babel/helper-validator-option": {
+      "version": "7.25.9",
+      "resolved": "https://registry.npmjs.org/@babel/helper-validator-option/-/helper-validator-option-7.25.9.tgz",
+      "integrity": "sha512-e/zv1co8pp55dNdEcCynfj9X7nyUKUXoUEwfXqaZt0omVOmDe9oOTdKStH4GmAw6zxMFs50ZayuMfHDKlO7Tfw==",
+      "dev": true,
+      "license": "MIT",
+      "engines": {
+        "node": ">=6.9.0"
+      }
+    },
+    "node_modules/@babel/helpers": {
+      "version": "7.26.0",
+      "resolved": "https://registry.npmjs.org/@babel/helpers/-/helpers-7.26.0.tgz",
+      "integrity": "sha512-tbhNuIxNcVb21pInl3ZSjksLCvgdZy9KwJ8brv993QtIVKJBBkYXz4q4ZbAv31GdnC+R90np23L5FbEBlthAEw==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@babel/template": "^7.25.9",
+        "@babel/types": "^7.26.0"
+      },
+      "engines": {
+        "node": ">=6.9.0"
+      }
+    },
+    "node_modules/@babel/parser": {
+      "version": "7.26.5",
+      "resolved": "https://registry.npmjs.org/@babel/parser/-/parser-7.26.5.tgz",
+      "integrity": "sha512-SRJ4jYmXRqV1/Xc+TIVG84WjHBXKlxO9sHQnA2Pf12QQEAp1LOh6kDzNHXcUnbH1QI0FDoPPVOt+vyUDucxpaw==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@babel/types": "^7.26.5"
+      },
+      "bin": {
+        "parser": "bin/babel-parser.js"
+      },
+      "engines": {
+        "node": ">=6.0.0"
+      }
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+    "node_modules/@babel/template": {
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+      "resolved": "https://registry.npmjs.org/@babel/template/-/template-7.25.9.tgz",
+      "integrity": "sha512-9DGttpmPvIxBb/2uwpVo3dqJ+O6RooAFOS+lB+xDqoE2PVCE8nfoHMdZLpfCQRLwvohzXISPZcgxt80xLfsuwg==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
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+        "@babel/types": "^7.25.9"
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+      "engines": {
+        "node": ">=6.9.0"
+      }
+    },
+    "node_modules/@babel/traverse": {
+      "version": "7.26.5",
+      "resolved": "https://registry.npmjs.org/@babel/traverse/-/traverse-7.26.5.tgz",
+      "integrity": "sha512-rkOSPOw+AXbgtwUga3U4u8RpoK9FEFWBNAlTpcnkLFjL5CT+oyHNuUUC/xx6XefEJ16r38r8Bc/lfp6rYuHeJQ==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@babel/code-frame": "^7.26.2",
+        "@babel/generator": "^7.26.5",
+        "@babel/parser": "^7.26.5",
+        "@babel/template": "^7.25.9",
+        "@babel/types": "^7.26.5",
+        "debug": "^4.3.1",
+        "globals": "^11.1.0"
+      },
+      "engines": {
+        "node": ">=6.9.0"
+      }
+    },
+    "node_modules/@babel/types": {
+      "version": "7.26.5",
+      "resolved": "https://registry.npmjs.org/@babel/types/-/types-7.26.5.tgz",
+      "integrity": "sha512-L6mZmwFDK6Cjh1nRCLXpa6no13ZIioJDz7mdkzHv399pThrTa/k0nUlNaenOeh2kWu/iaOQYElEpKPUswUa9Vg==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@babel/helper-string-parser": "^7.25.9",
+        "@babel/helper-validator-identifier": "^7.25.9"
+      },
+      "engines": {
+        "node": ">=6.9.0"
+      }
+    },
+    "node_modules/@bcoe/v8-coverage": {
+      "version": "0.2.3",
+      "resolved": "https://registry.npmjs.org/@bcoe/v8-coverage/-/v8-coverage-0.2.3.tgz",
+      "integrity": "sha512-0hYQ8SB4Db5zvZB4axdMHGwEaQjkZzFjQiN9LVYvIFB2nSUHW9tYpxWriPrWDASIxiaXax83REcLxuSdnGPZtw==",
+      "dev": true,
+      "license": "MIT"
+    },
     "node_modules/@esbuild/aix-ppc64": {
       "version": "0.21.5",
       "resolved": "https://registry.npmjs.org/@esbuild/aix-ppc64/-/aix-ppc64-0.21.5.tgz",
@@ -458,6 +742,16 @@
         "node": ">=12"
       }
     },
+    "node_modules/@istanbuljs/schema": {
+      "version": "0.1.3",
+      "resolved": "https://registry.npmjs.org/@istanbuljs/schema/-/schema-0.1.3.tgz",
+      "integrity": "sha512-ZXRY4jNvVgSVQ8DL3LTcakaAtXwTVUxE81hslsyD2AtoXW/wVob10HkOJ1X/pAlcI7D+2YoZKg5do8G/w6RYgA==",
+      "dev": true,
+      "license": "MIT",
+      "engines": {
+        "node": ">=8"
+      }
+    },
     "node_modules/@jridgewell/gen-mapping": {
       "version": "0.3.8",
       "resolved": "https://registry.npmjs.org/@jridgewell/gen-mapping/-/gen-mapping-0.3.8.tgz",
@@ -522,6 +816,13 @@
         "node": ">=14"
       }
     },
+    "node_modules/@polka/url": {
+      "version": "1.0.0-next.28",
+      "resolved": "https://registry.npmjs.org/@polka/url/-/url-1.0.0-next.28.tgz",
+      "integrity": "sha512-8LduaNlMZGwdZ6qWrKlfa+2M4gahzFkprZiAt2TF8uS0qQgBizKXpXURqvTJ4WtmupWxaLqjRb2UCTe72mu+Aw==",
+      "dev": true,
+      "license": "MIT"
+    },
     "node_modules/@rollup/rollup-android-arm-eabi": {
       "version": "4.30.1",
       "resolved": "https://registry.npmjs.org/@rollup/rollup-android-arm-eabi/-/rollup-android-arm-eabi-4.30.1.tgz",
@@ -795,6 +1096,64 @@
       "dev": true,
       "license": "MIT"
     },
+    "node_modules/@vitest/coverage-istanbul": {
+      "version": "2.1.8",
+      "resolved": "https://registry.npmjs.org/@vitest/coverage-istanbul/-/coverage-istanbul-2.1.8.tgz",
+      "integrity": "sha512-cSaCd8KcWWvgDwEJSXm0NEWZ1YTiJzjicKHy+zOEbUm0gjbbkz+qJf1p8q71uBzSlS7vdnZA8wRLeiwVE3fFTA==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@istanbuljs/schema": "^0.1.3",
+        "debug": "^4.3.7",
+        "istanbul-lib-coverage": "^3.2.2",
+        "istanbul-lib-instrument": "^6.0.3",
+        "istanbul-lib-report": "^3.0.1",
+        "istanbul-lib-source-maps": "^5.0.6",
+        "istanbul-reports": "^3.1.7",
+        "magicast": "^0.3.5",
+        "test-exclude": "^7.0.1",
+        "tinyrainbow": "^1.2.0"
+      },
+      "funding": {
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+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@ampproject/remapping": "^2.3.0",
+        "@bcoe/v8-coverage": "^0.2.3",
+        "debug": "^4.3.7",
+        "istanbul-lib-coverage": "^3.2.2",
+        "istanbul-lib-report": "^3.0.1",
+        "istanbul-lib-source-maps": "^5.0.6",
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+        "magic-string": "^0.30.12",
+        "magicast": "^0.3.5",
+        "std-env": "^3.8.0",
+        "test-exclude": "^7.0.1",
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@@ -893,6 +1252,28 @@
         "url": "https://opencollective.com/vitest"
       }
     },
+    "node_modules/@vitest/ui": {
+      "version": "2.1.8",
+      "resolved": "https://registry.npmjs.org/@vitest/ui/-/ui-2.1.8.tgz",
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+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@vitest/utils": "2.1.8",
+        "fflate": "^0.8.2",
+        "flatted": "^3.3.1",
+        "pathe": "^1.1.2",
+        "sirv": "^3.0.0",
+        "tinyglobby": "^0.2.10",
+        "tinyrainbow": "^1.2.0"
+      },
+      "funding": {
+        "url": "https://opencollective.com/vitest"
+      },
+      "peerDependencies": {
+        "vitest": "2.1.8"
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     "node_modules/@vitest/utils": {
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@@ -968,6 +1349,39 @@
         "balanced-match": "^1.0.0"
       }
     },
+    "node_modules/browserslist": {
+      "version": "4.24.4",
+      "resolved": "https://registry.npmjs.org/browserslist/-/browserslist-4.24.4.tgz",
+      "integrity": "sha512-KDi1Ny1gSePi1vm0q4oxSF8b4DR44GF4BbmS2YdhPLOEqd8pDviZOGH/GsmRwoWJ2+5Lr085X7naowMwKHDG1A==",
+      "dev": true,
+      "funding": [
+        {
+          "type": "opencollective",
+          "url": "https://opencollective.com/browserslist"
+        },
+        {
+          "type": "tidelift",
+          "url": "https://tidelift.com/funding/github/npm/browserslist"
+        },
+        {
+          "type": "github",
+          "url": "https://github.com/sponsors/ai"
+        }
+      ],
+      "license": "MIT",
+      "dependencies": {
+        "caniuse-lite": "^1.0.30001688",
+        "electron-to-chromium": "^1.5.73",
+        "node-releases": "^2.0.19",
+        "update-browserslist-db": "^1.1.1"
+      },
+      "bin": {
+        "browserslist": "cli.js"
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@@ -1311,6 +1892,39 @@
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@@ -1372,6 +1986,34 @@
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@@ -1398,6 +2040,16 @@
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@@ -1436,6 +2088,13 @@
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@@ -1672,6 +2331,19 @@
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+      "license": "ISC",
+      "bin": {
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@@ -1715,6 +2387,21 @@
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@@ -1879,6 +2566,34 @@
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@@ -1960,6 +2675,16 @@
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@@ -2485,6 +3210,37 @@
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+      "dev": true,
+      "funding": [
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+          "type": "opencollective",
+          "url": "https://opencollective.com/browserslist"
+        },
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+          "url": "https://tidelift.com/funding/github/npm/browserslist"
+        },
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+          "url": "https://github.com/sponsors/ai"
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@@ -2783,6 +3539,13 @@
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+      "license": "ISC"
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   }
 }
diff --git a/package.json b/package.json
index 60ff811..9126c6a 100644
--- a/package.json
+++ b/package.json
@@ -15,12 +15,17 @@
   ],
   "scripts": {
     "bundle": "tsup src/index.ts",
-    "test": "vitest"
+    "test": "vitest",
+    "coverage": "vitest run --coverage"
   },
   "devDependencies": {
+    "@vitest/coverage-istanbul": "^2.1.8",
+    "@vitest/coverage-v8": "^2.1.8",
+    "@vitest/ui": "^2.1.8",
     "tsup": "^8.3.5",
     "typescript": "^5.7.3",
     "vite": "^5.4.11",
-    "vitest": "^2.1.8"
+    "vitest": "^2.1.8",
+    "@types/vitest": ""
   }
 }
diff --git a/src/flatmatter.ts b/src/flatmatter.ts
index f152400..fc14699 100644
--- a/src/flatmatter.ts
+++ b/src/flatmatter.ts
@@ -138,13 +138,9 @@ export default class FlatMatter {
      * @returns {boolean}
      */
     private isPipedValue(value: string): boolean {
-        for (const part of this.composePipedValueParts(value)) {
-            if (!this.isSimpleValue(part) && !this.isFunctionValue(part)) {
-                return false;
-            }
-        }
-
-        return true;
+        return this.composePipedValueParts(value).every(part => {
+            return this.isSimpleValue(part) || this.isFunctionValue(part)
+        });
     }
 
     /**
@@ -188,12 +184,12 @@ export default class FlatMatter {
             return value === "true";
         }
 
-        if (!Number.isNaN(parseFloat(value))) {
-            return parseFloat(value);
+        if (!Number.isNaN(parseInt(value)) && value.indexOf('.') === -1) {
+            return parseInt(value);
         }
 
-        if (!Number.isNaN(parseInt(value))) {
-            return parseInt(value);
+        if (!Number.isNaN(parseFloat(value)) && value.indexOf('.') !== -1) {
+            return parseFloat(value);
         }
 
         return trimChar(value, '"');
diff --git a/src/serializers/to_object.test.ts b/src/serializers/to_object.test.ts
index 24fc54f..7059458 100644
--- a/src/serializers/to_object.test.ts
+++ b/src/serializers/to_object.test.ts
@@ -48,7 +48,7 @@ test("Simple function usage", () => {
     }
   }
 
-  const fm = new FlatMatter('a: (to-upper "value")', [new ToUpper()]);
+  const fm = new FlatMatter('a: (to-upper "value")', [new ToUpper]);
   const config = fm.serialize(new ToObject());
 
   expect(config).toStrictEqual({
@@ -65,7 +65,7 @@ test("Piped function by reference usage", () => {
     }
   }
 
-  const fm = new FlatMatter('a: "value" / to-upper', [new ToUpper()]);
+  const fm = new FlatMatter('a: "value" / to-upper', [new ToUpper]);
   const config = fm.serialize(new ToObject());
 
   expect(config).toStrictEqual({
@@ -82,10 +82,85 @@ test("Piped function by call usage", () => {
     }
   }
 
-  const fm = new FlatMatter('a: "value" / (to-upper 123)', [new ToUpper()]);
+  const fm = new FlatMatter('a: "value" / (to-upper 123)', [new ToUpper]);
   const config = fm.serialize(new ToObject());
 
   expect(config).toStrictEqual({
     a: "VALUE-123",
   });
-});
\ No newline at end of file
+});
+
+test("Invalid value in pipe", () => {
+  const fm = new FlatMatter('a: "value" / / asd');
+  const config = fm.serialize(new ToObject());
+
+  expect(config).toStrictEqual({});
+})
+
+test("Invalid value in pipe, 2", () => {
+  const fm = new FlatMatter('a: "value" / asd');
+  const config = fm.serialize(new ToObject());
+
+  expect(config).toStrictEqual({
+    a: "value"
+  });
+})
+
+test("Only piped functions", () => {
+  class FirstFn implements FlatMatterFn {
+    name = "first-fn";
+
+    compute(input: string): unknown {
+      return input.toUpperCase();
+    }
+  }
+
+  class SecondFn implements FlatMatterFn {
+    name = "second-fn";
+
+    compute(input: string): unknown {
+      return `${input}-passed-by-second`;
+    }
+  }
+
+  const fm = new FlatMatter('a: (first-fn "value / here") / second-fn', [new FirstFn, new SecondFn]);
+  const config = fm.serialize(new ToObject());
+
+  expect(config).toStrictEqual({
+    a: "VALUE / HERE-passed-by-second"
+  });
+});
+
+test("Function call without any args", () => {
+  class ToUpper implements FlatMatterFn {
+    name = "to-upper";
+
+    compute(input: string): unknown {
+      return input.toUpperCase();
+    }
+  }
+
+  const fm = new FlatMatter('a: "value" / (to-upper)', [new ToUpper]);
+  const config = fm.serialize(new ToObject());
+
+  expect(config).toStrictEqual({
+    a: "VALUE",
+  });
+})
+
+test("Function call using multiple strings with spaces as arg", () => {
+  class ToUpper implements FlatMatterFn {
+    name = "to-upper";
+
+    compute(input: string): unknown {
+      return input.toUpperCase();
+    }
+  }
+
+  const fm = new FlatMatter('a: (to-upper "value goes here" "and here")', [new ToUpper]);
+  const config = fm.serialize(new ToObject());
+
+  expect(config).toStrictEqual({
+    a: "VALUE GOES HERE",
+  });
+})
\ No newline at end of file
diff --git a/vitest.config.ts b/vitest.config.ts
new file mode 100644
index 0000000..f8afc15
--- /dev/null
+++ b/vitest.config.ts
@@ -0,0 +1,12 @@
+import {defineConfig} from 'vitest/config'
+
+export default defineConfig({
+    plugins: [],
+    test: {
+        globals: true,
+        coverage: {
+            provider: 'v8',
+            reporter: ['text', 'json', 'html', 'clover']
+        },
+    },
+})
\ No newline at end of file